Hello. Just purchased the HS220 dimmer. I wired it up like it should in my bedroom. However, I have the bedroom lights, hallway lights, stair lights, and bathroom lights on the same circuit. (They all are different rooms with their own separate switches, but same breaker)

I only want the dimmer to work the bedroom lights. NOT all the other lights on the circuit. (AKA the hall and bathroom lights.)

When I wired the dimmer in the bedroom I noticed 4 white neutral wires marretted together. I assume they are the neutral wired to the other lights. 
 

so how do I wire it so the dimmer ONLY works in the bedroom and not affect the other switches and lights??

please help!!!!