Did you just hit 80? Do you have the correct rotation down? How geared are you/What're your stats? As FFB spec, 2700 DPS isn't good in 25 man-- however, FFB is very gear dependant. Usually you want to have at least 30% crit before buffs(before molten armor) for FFB. Obviously, you also need to be hit capped.
I can't help much more without looking at your Armory.
Edit: If your first raid was a 25man Vault, you probably aren't geared enough for FFB. If you don't have all the staple heroic/emblem gear, I would re-spec Frost and just do heroics until you're mostly heroic-geared. If you still aren't ready for FFB by then. spec Arcane and PUG raids. I'll say this, though, 2700 DPS is better than most PUGs. Especially if you're just fresh 80, lol.