need help please
 

I just got a JR XS3 and i put it in my revoo but it wont steer all the way on both sides.

Have a good read of your radio manual. In particular, take a look at the EPA, ATV or ATL features. Your radio should at least have some of these features, if not all.

You need to adjust your radio so that you get the travel you need, whilst ensuring that your servos are not stalled by trying to operate the steering and throttle mechanisms past their mechanical limits. Stalling your servos will damage them (you'll most likely blow the IC or break the gears) and you'll draw excessive current as a result.

You may also want to set your servo's neutral with the 'subtrim' function. This is especially useful on the throttle servo.

You can also adjust your steering from 0% - 125% check this is at least 100%