Sign out, remove your profile and then sign back in.
If you are having trouble with a specific website we have a video that walks you through some additional steps.
The final option is to take it to your school library and they can factory reset it. If you try to do this on your own it will not work because you will need a staff member to sign into the Chromebook after it restarts.
(Staff: Any staff member can powerwash a Chromebook by pressing ctrl,shift,alt, and r all at the same time. After it restarts you then need to sign in to the Chromebook so it will be enrolled. Then the student signs in like always.)