MovieClip view area

Good day
Could you advise me, how can I set a movieClip display area?
I got mask animation in my clip, so full width is about 1800px. My Mask got 800. In a fact I see that 800px area, but if I am tracing that Clip width- that gives me 1800.

The problem is, that when i change a screen display state to FullScreen and back to Normal , my project moves to the side and that look horrable

Is it possible to set my clip width and height to my own properties, but not depending on mask animation in Clip?