Ok...First, what are you doing playing between the black keys? There are only a very few crazy exercises that require (almost) you to put your finger there.

ok i know i know its not a inch but you have to have really chubby fingers to get stuck.

Harvey what do you mean crazy exercises?

You see, this is the problem.

My fingers get stuck when playing in the cracks between the black notes when I extend my hand..

For example, if with the right hand I`m playing middle C with the thumb, and I stretch the little finger to play the C# an octave to the right. And when I play the white notes, C & B, descending, with the fingering of (4) and (3), between the black notes, the fingers get jammed in there, and the surrounding black notes go down with them.

I noticed that when playing stuff like this, my fingers flatten out, especially when swinging from the C to the C# as I mentioned. What can I do to avoid this so that my fingers don`t get stuck like that when playing between the black notes, or is this something I shouldn`t even be worrying about?

then i suggest you dont try to stick your fingers between the black key. just put your finger on the white bit that is the fattest part.

Wait a minute..I read something fishy in there...Div, do u mean that when u play Middle C, C#, C, B with fingers 1, 5,4,3 u get stuck? Is that what yr trying to tell us..That yr fingers get in their own way? Then may I know...are u still holding on to yr C# when playing C and B and fingers flat down moreover? Or yr finger 5 is still laying there when the finger 4 is trying to squeeze in? If that`s the case, then that`s why yr fingers are clumsy. Try lifting them up one by one and curve or play with yr finger tips... Don`t jam in so many fingers in ine same place.

How I would finger that: (But really, are you fingers that big?)
C C# C B
1 4 5 [if your C# is still held then 3, if not then 4]

Sounds like you`re playing one of those small Casio type keyboards - should never have a problem with a proper size keyboard or piano....
Maybe you`re playing the black notes too far in....?
PETE W