Something tells me you literally just dash dance in place and don't go anywhere with it. Don't do that. Flick the stick, and let it return to neutral. You can then keep going in the direction, change directions, whatever. Don't just rapidly press left/right, that's stupid and does nothing for you. It doesn't evade, it doesn't have any offensive properties, just quit it.
Running in this game has two animations. The first one is the relevant one. Any time during that animation, you can turn around instantly, or you can just let it end and press that direction again. AND there's like 2 frames where you're actually standing in neutral when you turn around, so you can C stick a Smash attack or get a grab in neutral without worrying about doing a dash attack on accident.
If you accidentally go into the second running animation, you'll know real fast when you try to change directions. You'll slide for like 5 years before actually turning around. Dash dancing allows you to skip that altogether. Just do it. Unless you're Jiggs, then like, idk man, jump or something.