When I try to do a tap jump for an ariel attack while still above the ground like with Fox's shine and Marios Fireball. I either end up going higher then Im supposed to or I do a Uair. Any advice? If I posted in the wrong sub forum I am really sorry

You can't tapjump/shorthop with your midair jump. It's always a set height.

What do you mean? I meant like how do I Short hop without mucking up or like accidently doing a UAir.

Cstick is always an option, I personally just switched to tap jump off and set a separate button to jump. Even when I use controller I leave tap jump off in SSF2. I don't think there is a practical way to do SH uair with tap jump off, and if you want to do falling uair without jumping you'd have to be pre-holding up or have no jumps left or something. Either way, much more difficult and very restrictive.

But tbh im a little confused by your wording lol

if you mean you're on the ground and accidentally fullhopping/doing an uair:

for shorthops you just gotta tap the button really quick. practise makes perfect
for shorthop uairs, I recommend using a c-stick button. you can set this to whatever you want in the controls menu

c-stick allows you to do aerials (when in the air) or smash attacks (when on the ground) without pressing the attack button.
for example, c-stick up allows you to do an uair or usmash.

Its possible to do sh uairs with tap jump, I've been doing it consistently for a while. Basically you just tap up then do up air quickly after. That's really the best I can explain it lol. Cstick buttons also work but I'm to used to doing it the way I said xD

short hop is when you release the jump button in a charecters jump animation