Technically when you’re a closer you leave when the shift is done with everything. They’re not allowed to enter or leave the store alone there must be another partner with them. You’re probably not going to get in trouble for staying 15 minutes late as a minor but you probably should’ve checked in and see if it was ok to leave. Even going “hey I did finished up those tasks you gave me do you need anything before I head out?” Is a good way to maybe print that you need to go. Personally I don’t leave until my shift tells me to unless my day is shit and need to get out then I ask.