teeth and blowjobs

What do you do with your teeth while you're giving a blowjob?? I know you're supposed to like cover them with your lips or something but when I have something big in my mouth and I'm almost gagging it doesn't seem to work. I've practiced blowjobs with my dildo and I don't know if my dildo is just too big or something but I have trouble keeping my teeth out of the way. I've given a real blowjob once before but I was 15 and have no idea if I did it right lol. I'm seeing my boyfriend in a few weeks and plan on giving him head but I'm terrified that I'll scrape him with my teeth and he won't enjoy it. I have terrible anxiety so I can't stop worrying about it lol