Piano Forum

Ideally you'd work on this with a teacher, but I'll try to communicate the gist of what I think is needed.

Right now, it looks like you are restricting your hand to only stay over the white key area of the keyboard, so you kind of have to stretch out your 4th finger forwards in a tense way to reach the black key. You don't need to exaggeratedly move your hand in and out to correct this, just allow it to be free to move in all directions horizontally as needed to assist your fingers.

Try this:
1. Let your hand and arm hang relaxed by your side, like when you are just leaving it alone and letting it be when you are not doing anything with it.
2. Bring the hand to the keyboard like when you are about to play, but keep it in the same state and shape as it had in step 1.
3. Where do you need to place your hand to have the 4th finger conveniently placed to play the black key without stretching it forward or otherwise modifying the shape of your hand? Chances are this is a bit further in than where you currently are when you play it.
4. When you play the white keys, you can let your hand smoothly move out a bit from the black key era to have the fingers conveniently placed for the white keys instead.
5. Adjust as needed when you play the scale but keep the hand in a neutral state and shape as your default mode. Move the hand rather than stretching out forwards with your fingers. You are already moving it laterally and up and down so you just need to allow yourself to move horizontally too.