This will take some time but do this-it is exactly what a locksmith will do from the start.
Work your combo as normal but instead of your normal numbers go +- one or two numbers each way from the normal. It is pretty common for the tumblers to shift a bit if the safe is jarred or if you throw the dial hard and fast when your unlocking it.
Go slowly and methodically, one number set at a time. Keep notes and go slowly.