Thank you,
I would say that if you're starting out on the idea, getting it done in the next few days could be hard, but go for it if you want to. You can go ahead and use code from this one if you can understand it, though it's super compressed. Here's a really useful piece, though, that's slightly simplified from the version in the cart.
ˇ-=4b=btn()p+=b%4-b%2*3if(b\9*ˇ<0)x=p+2ˇ=k
That one line contains basically all the logic for the movement of both the player ship and its projectiles. I'll break it into a few parts to explain.
ˇ-=4 This moves the single player bullet up 4 pixels every frame. The "ˇ" symbol, which represents the bullet's y position, doesn't have to be initialized because before it's given a value, it already has a negative one. (it's the only symbol like this that doesn't count as two chars on Twitter, though, as far as I know).
b=btn()p+=b%4-b%2*3 This moves your ship's horizontal position, "p", using the left/right keys
if(b\9*ˇ<0) This allows a bullet to be fired if the last one is off screen and you press the Z or X key (well, there's only one, so it lets it be re-fired).
x=p+4ˇ=k This aligns the bullet x and y positions with those of your ship (represented by p and k), putting it in firing position. Since it automatically moves up, it looks like it's being shot.