Just ask him! Go for it. You only live once, might as well have some fun. Take a risk. If you don't, you'll beat yourself up for not doing it because what if he would of said yes?!
Unfortunately, there is no guaranteed way to ask him that will make sure that he will react in the perfect way. There is always a risk that he will either feel like you are more of a friend and he might feel a little uncomfortable, or that he might go with you and it might make you both feel uncomfortable later.
However, if you really, really like this guy and are willing to take that risk, then, hey, go for it! You have to be prepared for either possibility, but when you feel something special, it is worth the risk.
I would just straight out tell him that you think he should go with you to the dance. You don't have to even tell him that you want it to be as a date--you can just see how he reacts first. If he acts uncomfortable, you can say that you should just go as friends, if not, then just see where it takes you. Be ready for anything, and keep your cool no matter what happens. Good luck!
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