Hi, I've had a great many CT scans and I've always been allowed to keep my watch and glasses on. It will depend on what part of you is being scanned whether they ask you to remove jewellry. For example, if it's a scan of your head they the earrings will probably have to go.
You do wear a gown, and they sometimes give you a contrast either to drink or through a canula.
Every one I've ever had has been over in five minutes. It really isn't a problem.
(Perhaps you're confusing it with an MRI scan, where they do have to take metal from you).