when i was at ur level i was struggling too. my best suggestion is to go outside of the temple (if possible, i don't kno, i had another saved game) and level up. there are red fiends that comes in groups of 3 and 6, which give a good amount of exp. i would say i trained to level 40, which raised my speed. after that Demon's Gate was a sinch.

if u don't feel like leveling up, try using haste and wall (if u have it). also, make sure aeris is ur healer. then,simply use limit breaks, along with bahamut.