Dead Space 2 Zealot Final Boss

I've playing through the 3 main games again (Xbox 360, if it matters), and I'm stuck at the end of Dead Space 2. There is simply nothing I can do to beat Nicole and destroy the Marker. I had no problem beating it on Normal back when it came out, but the final boss battle seems extremely unbalanced on Zealot.

The main problem is my lack of ammo, med packs (along with stasis, but that's not as big of a problem), and the right guns. I overwrote my save at the last store, so the only save I have is at the last save station. I did manage to run all the way back to the store once, but it is just not worth it. I don't have too much credits, so I can't buy enough ammo and health to make the trip back. If there was a store right before the boss battle, then it would be more doable.

I've wasted hours trying to beat it, and I really don't want to lower the difficulty, cause everything I've done would've been for nothing and I'd have to replay it again. I don't see why there hasn't been a patch for this, cause it's obviously a problem. I'd just like some help since I really want to start my Hardcore playthrough. Btw, I only have a Plasma Cutter with I believe 20 shots and a Pulse Rifle with 90 or so rounds.