As someone who fits in but used to be an outcast, I can assure you, fitting in isn't about having mainstream hobbies, but proactively talking to people.

I still find going up to people and talking to them to be kind of scary, so the method I used was to join a college association I was interested in.

As for your hobbies, there is nothing wrong with having obscure hobbies, in fact, it makes for a great conversation topic. And unless your hobby is really out there, you could probably find a group that enjoys your hobby.

Of course, this assumes you have access to such spaces, which is not true for everyone.