I'd like to say you choked... but I have to admit I also get tight when I have a good round going.... say double-digits under par after 12 or 13. I know people like to get on the restart hamster wheel and under no circumstances keep going unless they're at least 29 at the turn.
Hell, many people will restart unless they're at least 27 or 28! Frankly, I've so far only fired a 28 in the front once. If I took that kind of attitude I'd never get the chance to see the back 9, let alone learn it.
But I try to complete as many rounds as I can, sometimes making the turn at 30 or 31. As a result I'm getting a little handle on how to play the back 9... fired my fair share of 59s and 58s. Then patience paid off, got a 57 on Monday and a 56 on Tuesday... both times firing a 30 on the front and birdieing 15 through 18 to finish.
Good luck!