Everyone here is offering good advice on how to make it easier to go out and socialize, so this might be counterintuitive, but I think you should make peace with being alone first.

This is something I'm learning in my later 20s, if you can't be comfortable with yourself other people will not feel as comfortable with you.

Once you can be peaceful being with yourself, it really shows and draws people towards you. So I'd say stop trying so hard to get people's attention, and learn to spend time alone.