My mouth is too small!

I'm in college and I've recently starting branching out and having some (safe) fun with guys on campus I meet on Tinder. Sex hasn't been a problem but whenever I try to hook up with a guy and they ask for a blowjob, their penis won't fit in my mouth. I feel like I could really be good at it but even when I open my mouth as wide as possible, there's maybe an inch and a half of space between my top and bottom rows of teeth. Has anyone else had this issue or have suggestions to help?