An adult turtle can take up to 6 months to shed - even more if there's pyramiding. Easter once had a scute hang on for a year.

Just make sure there's no algae under the scute. You'll be able to see it if there is. It will come off in its own sweet time.
You can also offer "scratching posts". I have PVC pipe (with a cap) stuck down in the tank for the sole purpose of Easter being able to scratch on it. He gets UNDER his little bridge and scratches. Then sometimes he'll leap out of the water, bite onto the air hose and use it to hold himself while he scratches against the dock!

The point is, you can offer places for him to scratch so he can do so at HIS leisure.