I was a swimmer in college and we had no divers on the team my senior year, so I filled in a couple times. I could do front flip and backflip and inward, but I tried a gainer once and landed flat on my back, the whole stadium made that noise "ohhh". And that was the last time I tried a gainer. My buddy was in the stands and he was a diver the previous years, and he said the same thing you just did.
Spiraling off topic, but the summer I decided to learn a gainer (about 5 years ago) I convinced a friend who is equally game for bad ideas to try them with me.
I was sitting at the pool with the family and bemoaning the fact that I could do front flips and back flips but gainers had always eluded me and that at 40-whatever years old I was at the time, I was annoyed that I wouldn't ever learn them.
My friend who's a few years younger and was a pro soccer player and is generally up for whatever was easy to talk into "we keep going until we do one... today."
My first attempt went 45 degrees off the diving board into a back dive, and as I was spotting my landing I realized I was heading right into the concrete edge of the pool. I heard gasps and a small scream as I cart-wheeled for the edge, but somehow slipped into the water without broken bones.
Friend lands straight on back.
We're 4 minutes into this HUB adventure and both looking grim.
Second one I pull around to land on my stomach and the 15 year old lifeguard yells, "you gotta reach straight up first!"
I go straight towards the afternoon sun with my hands, pull knees to chest and rotate a 1/4 turn sideways, and take the face shot of my lifetime to the side of my head.
A 2x4 to the face would be the physical representation of this one.
Float to the edge of the pool with my tears hidden in the chlorinated pool water.
At this point, my buddy is sitting on the edge of the pool claiming head trauma.
...
At this point, I'd like to point out that I'm on a 5' high spring board. This is the mildest most pathetic situation I've been a part of. My wife is literally unable to watch.
...
Next attempt. Full bounce. Hands "feel" like they're reaching for the stars, knees to chest, head straight back... and I slip into the water like it is no big thing. I then do about 15 more in a row to make sure I don't forget how to do it.
So all this is to say that I feel your pain of trying a gainer, in front of a crowd and taking it to the chin.