you sound like a teenager.
Just walk up to the person, ask them out, and if they say no, forget about them.
If they say yes, see if it works.
IF you don't know if they like you, you likely don't actually know who they are, and thus shouldn't claim that you like them. It sounds like you haven't really even talked to the person that much.
Puberty sucks, we've all been through it, just get over your fears and take the risk. If it fails, screw it - you have your whole life ahead of you to find new people.