Mains problems are:
1) Two drops are shit. They make no impact on the game.
2) Too many spells. Most creatures seem to be Searing Spear immune in some way with "Don't kill me" effects or 4/4.
3) Mana Flood/Mana Screw happening too much and even Creature Screw when it's 1/2 my deck. I suspect that it's my shuffling as I'm copying mana curves from tournament winning aggro decks with 19-21 lands, but don't want luck to be an excuse for my bad performance.
4) I could play better, I am sometimes a turn off winning. Main thing is waiting for them to be tapped out before trying a game winning play - I did this in my last game and won.
Part of it is that you're new to the game. You'll get better. A couple suggestions though, all of which assuming you want to stick to Boros:
1. Doomed Traveler is used in Aristocrats lists because of sac outlet shenanigans with Cartel/Falkenrath Aristocrat. Playing Boros, you have no need of him. It's a fundamentally defensive creature unless you have a way to exploit it having two bodies. Stromkirk Noble will perform MUCH better for you. He'll also give you a turn 1 red play.
2. Some people like Firefist Striker, but I don't. It only shines in aggro vs. aggro matches where you want to push past blockers, and it dies far too easily. That's okay for Lightning Mauler since at least it'll give another critter haste. Consider Ash Zealot instead. It has haste, first strike makes it much more survivable in the early game, and it passively fucks with graveyard shenanigans without costing a sideboard slot. It's a cheap rare, and very worthwhile in a list like this.
3. Another option if you drop the spell count and play more creatures is Thalia, Guardian of Thraben. She buys you another turn to kill your opponent vs. control and midrange, and tends to protect your other creatures by being the first thing they kill. At a minimum, she deserves 3 spots in your sideboard.
4. Rally the Peasants is cute, and I used it to good effect in a R/W/B tokens deck I played one weekend, but there are better uses for that slot here. If you really want a pump effect, consider Legion's Initiative. It'll give you a smaller bonus, but it's persistent, and gets a lot of your creatures up to the key 3 power needed to push through common blockers like Augur of Bolas. Loxodon Smiter will still be a problem, however, so we'll tackle that another way.
5. This is definitely aggro, but it isn't a blitz deck and you need a slightly better top end. Anything x/4 or better is going to be a brick wall to you. I know you like them, but consider dropping Silverblade Paladin. He's very powerful, but he also encourages some poor decisions than can leave your ass flapping in the wind (i.e. attacking with a bonded creature thinking it is safe, only to have the Paladin nuked out from under you, forcing a loss of the second creature to a suddenly lethal blocker). Frontline Medic is actually a lot better at getting damage through because it gives your creatures some persistence. I'd drop all 3, up the Frontline Medics to 4, and add:
6. Hellrider is a god for this deck. He's not reliant on battalion but fits perfectly in line with what you're doing (overextending on the board to push through lethal before they can stabilize the board). The damage he causes is very difficult to prevent, since it comes from multiple sources, and he'll very often get the final bit in before the attack even resolves.
7. You are playing too few lands, and guild gates are unnecessary in this deck. You do NOT want a land coming into play tapped on your first 4 turns in this deck, ever. It's very likely game over for you if you don't consistently drop a threat on your first 3 turns. Up this to 21, or even 22. Keep the sets of shocks and check lands, and then determine the rest of your curve by adding up all the colored symbols and dividing each by 2. You want roughly that many sources of each color at minimum. You're likely to run more heavily red than white assuming most of the suggestions here, so I suspect it will lean that direction.
8. Blasphemous Act is only there for free wins with Boros Reckoner on the board, but it isn't your main win condition. You can afford to cut these down, or even remove it entirely if you're not comboing off every third or fourth game. It does work splendidly with Frontline Medic, however. If you do remove any of these, consider Mizzium Mortars. It gives you an early answer to Loxodon Smiter and other 4 drops, and if the game runs long can function almost as well as Bonfire of the Damned as a one-sided wrath effect.
Overall, I'd try something like this:
Creatures (30)
4x Boros Elite
4x Champion of the Parish
4x Stromkirk Noble
4x Ash Zealot
4x Lightning Mauler
4x Frontline Medic
4x Boros Reckoner
2x Hellrider
Spells (9)
4x Searing Spear
3x Legion's Initiative
2x Boros Charm
Lands (21)
4x Clifftop Retreat
8x Mountain
5x Plains
4x Sacred Foundry
Sideboard (15)
3x Thalia, Guardian of Thraben
3x Nearheath Pilgrim
1x Blasphemous Act
3x Mizzium Mortars
2x Oblivion Ring
3x Skullcrack
I haven't goldfished it, but that should be able to clock 20 damage by turn 4 a little more reliably, and maybe give you enough stubborn cards on the board to live through a midrange sweeper. Give it a shot.