You cannot guarantee that a continuous rotation "servo" will stop when commanded to, but you may be lucky and be able to use servo.write(90); or something close to it. It may be better to use servo.writeMicroseconds(1500); as it allows finer control
If you don't care what angle the "servo" stops at then why use a servo in the first place ? How important is it that the "servo" stops at the same angle as it started ?
Perhaps if you explained exactly what you are trying to do it would help