Yes, it's possible to get in with your GPA. It also depends upon where you're applying, but, I think many of the schools - if you check their admittance stats - will show acceptances with GPA's lower than 3.4. Their average may indeed be higher, but, yes, a 3.4 is possible.
Prepare for the GRE and don't take it until you're feeling at least fairly confident. Once you take the exam, and accept the score at that time, that score is on your record. Even if you perform better on a re-take, the previous scores are still on record. Each school varies on which score(s) they'll consider, but, when you take the exam, you want to make it count as best you can.
A really sweet GRE score can do alot for a below-average GPA in many cases, apparently. So do your best on it, and be sure to practice the exam prior.
Good luck!