Does practicing a musical instrument on Sunday count as work?
Please talk to your pastor. You seem to think a lot of things are sinful, perhaps you should discuss scrupulosity with your pastor.
Arguably, it’s a leisure activity.
My teacher tells me to play on Sunday not practice
Playing a musical instrument seems to be what some would do for enjoyment. Why would you think this as work. One must do things on Sunday otherwise you would be required to just sleep all day which would be ridiculous. Just relax and use your common sense when thinking whether you’re sinning or not. God is not so particular that he is trying to catch you doing something wrong. He’s on your side not against you.