Accepting a friend request from someone you don't know is never a good idea.
It might be nice to have loads of 'friends' on social media but they aren't really friends if you don't know who they are.
Even though you have made the right decision, you should tell a responsible adult about what happened. It might be one of your parents or a guardian.
Remember, you can always contact the police on 101 if you have any concerns.
In an emergency always dial 999.