Don't tell him! If he is a shy guy that will just make him really nervous! Also if he doesn't like you back and you go up and tell him he might not have to heart to tell you he doesn't like you which will just lead to heart break later on! Just go talk to him normally like you would to your friends! Ik it's hard I've done it many times! Tell me how it guys gurl! Slay!
If you mess up just laugh it off! Guys like girls that aren't to serious about themselfs! Be yourself! It will only cause more problems later if you pretend to be someone your not! He'll like you for you not for who your pretending to be!