I have feelings for someone I may not see again

I recently graduated, and throughout the entire school year I had feelings for this girl. We talked during school sometimes and we follow each other on all social media platforms, I'm just not sure how to approach it. I feel that she would find it weird if I just messaged her, so I haven't done that, and I can't seem to get rid of the feelings I have for her so I'm really unsure of what to do about it.

I would send her a message: Hi X, Now that school's over, I miss seeing you around. Was wondering if I could treat you to lunch sometime. (or whatever other activity you might want to ask her to join you in)

You can't predict what she will think. Maybe she won't be interested but her ego will be boosted. Maybe she will be thrilled, because she has a crush on you, too. If you don't take a chance, you will regret it. If you take a chance, you have a 50 percent chance of success, which is better than 0 percent, if you don't try. If she's not up to the meet up, at least you can feel good you tried and be able to move on, and know that your fate lies elsewhere. Good luck!