There are no known cheats, if you find yourself short on xp see if there are any side quests or areas you've missed. Where you go is pretty open so if one area is too hard there's likely another more your level.
As far as levelling goes, I'm level 17 now and have found it pretty much spot on the whole time. Sometimes I'd enter an area a couple of levels above me, but then later I'd find one I'd missed that was now a level below me.
