68° - Is that the liquid temp or ambient? If ambient, the liquid is probably a good 5° or so higher during active fermentation and that could get you some unwanted banana or other fruity esters.
As far as whether your beer will be a banana bomb? It's hard to say, maybe, maybe not. The fact that the banana is coming out of the airlock suggests that the banana is being scrubbed out by the CO2, so you may be okay.
Edit to add: Dry hopping will cover up a lot of sins, so doing so would probably provide some decent anti-banana insurance.