I think you should be fine to just back them off, do the last two stages again. You haven't hit the "right" torque values on the way up last time, and if you are as low as you think you are, you probably haven't started to yield the bolts. if you have started to yield the bolts, they should be only "just" started, and I can't imagine that backing them off and bringing them all the way to their proper torque would be worse than just doing it right the first time.