Hi there, Soleil_,
Thanks for visiting the Apple Support Communities. If we understand, you signed up for the 3-month free trial of Apple Music, but forgot to cancel the subscription. We're happy to provide you with some information!
Subscriptions cancel at the end of the current billing cycle. That means if your Apple Music free trial expired three days ago, and you did not cancel, you were charged for the next month's membership. If you cancel now, you will still have access to Apple Music, your library, etc, through the end of the billing cycle.
In order to prevent being charged for the next billing cycle, you must cancel your subscriptions with no less than 24 full hours before the date of renewal: How to cancel a subscription from Apple - Apple Support.
Best!