It is possible to finish the game on level 31 (or even 30), though the last fight in the hall of echoes is going to be more of a challenge than the beginning.
If you are relatively close to going up a level you could try running around the fjords and see if you missed anything (check your quest log). You could max Wisdom first, and then re-skill before returning to the hall of echoes (you'd have to be pretty close to level 32 for the Wisdom bonus to make a difference, though).
Have you lowered the difficulty setting in the game options, if you are not already playing on easy?
Fly around first and take out a few of the opponents before heading to the nests. If you keep moving you can just use Fire Sphere and stay fairly safe. Rotate around any flying opponents or nests you use Fire Breath on, so you are not a sitting target.
Fly high back towards the start (where there tend to be fewer opponents) to heal, then turn and make another run through. Whenever you take out a nest and survive, save the game (keep the last couple saves, at least); after that there will be fewer opponents, and you can make progress faster.