I did the blue hole with only OW certification and about 30 dives under my belt and it was fine. I thought it was a really cool dive, by the way. The cave formations, sharks and deep blue water are like nothing else I've ever seen.
I think I was really pushing it with that amount of experience, though, and probably wouldn't do it with if I were in your shoes. If you have excellent buoyancy, are 100% comfortable in the water and think carefully about what might go wrong at that depth and how to deal with it, I say go for it. If you have even a little heistation about any of those things (espeically the buoyancy part), you should skip it for another day.
Even if you don't do the dive, you may want to go on the trip with your friend anyway. You can snorkel while they dive the BH and then participate in the great picnic lunch and other two half moon caye dives that are typically offered on the trip. The two dives we did on half moon caye were suitable for beginners and were probably my favoite two dives on my trip to Belize.