Hi Ella
I’m a high school student with ADHD and i love playing piano but the same thing happens to me too. What I try to do is decide what music to play before i start practicing. Ex. Ill play song 1 first, song 2 sencond ect. Ill all decide how many times I’ll play each song and usually i move the other songs somewhere else so I don’t get distracted by them. If your taking lessons then your teacher can defined help with this.
Hope you are successful in all your piano endeavours. 😊