Its looking good, and I lost 2 xacto knifes for not sharpening them very good, *they were bent out of shape, and the other I couldn't even cut paper
It's likely time for you to get a new knife. I worry as to what you're trying to cut if you've managed to bend a knife so badly, and how you're trying to cut it - perhaps it might be worth looking into acquiring some disposable snap-off blades if you're going to be working like that. They're cheap enough to buy, the refills aren't incredibly expensive, and if you buy a decent one, they'll last you for years. I've had my current one for about three years.
I'm planning to use a drywall
...as in, the construction material? I... ech, I'd honestly try to steer away from using something like that. Take it from personal experience, that stuff isn't pleasant to work with. I recently had to patch up a hole I knocked in my partition wall, and it's really not fun to cut and shape. If you're thinking of making prop weapons, I'd suggest layered/sliced cardboard builds - it's cheaper, more forgiving to work with, and probably lighter to handle in the long run.
I'm gonna try to but cardboard besides them and make it just a bit more flexible, or durable, and then fiberglass it, or add Eva foam...
Pick one material and work with that to the best of your experience, rather than trying to get technical and working with multiple mediums at once. I mean no offence at all, but you're really in need of some experience before you try anything complex, so I'd suggest, as above, trying a sliced/layered cardboard build. You could also research EVA foam weapon builds - I've seen several decent EVA foam weapons knocking around.
And I'll echo
Sandbagger regarding fibreglass - it's not a good material for beginners to use, and mistakes with it tend to end up messy, expensive, and very difficult to correct. By all means, I'd encourage you to experiment and get some experience with it, but I'd suggest trying it on a smaller, less critical component first, such as an armour shin or a shoulder plate.
but I most likely won't be right, since I'm both trying to make it flexible and heavy/hard... which is never a good combination...
Drywall isn't exceptionally flexible - none of the materials you've listed, aside from perhaps EVA foam, are. Ideally, your prop weapons won't flex at all, and will be sturdy enough to withstand light impacts. Again, mirroring
Sandbagger, you can always add weight later through metal pipes (which, again, will add structural strength and rigidity), electronics, or even well-placed wooden blocks will suffice.
I would urge you to perhaps do a little more research before heading back into this project. Your enthusiasm is admirable, I'd just hate to see this project fail and have you end up discouraged from it. Good luck, regardless.