Take a little advice from an old man. At least 80% of life's regrets come from the things you _didn't_ do. "I wish I had asked that girl I liked in school out", "I wish I had taken that trip when I had the chance", "I wish I had spent more doing X" or "... spent more time with Y" and so on. So, yeah, if you like someone and wonder if you should ask them out, do it. The worst that happens is they say 'no'. Sure, it will hurt for a time but you'll get over it. At least you won't be spending the rest of your life playing "what if...".