I remember how nervous I was when I was going to ask my father in-laws permission. I had a stomach ache all day and in the end everything went great! It's just a matter of not getting yourself psyched up too much before. Just be polite and to the point I guess. I was 19 when I asked permission which seems crazy to some people I guess, but here we are 2 1/2 years later with an extremely happy 9 month old baby girl. You'll be fine man, you got this!
edit, I see I was a little late in posting this, but congrats!