position the CTI (current time indicator) in the timeline to be on the keyframe that you want to keep. then turn of the keyframes (click the stopwatch). the current state of the mask will now be set and will not change unless you keyframe it again.
It seems to me you need a little basic training in After Effects -- from the PROS, and not some high school kid on youtube. High school kids gloss over or totally miss important points. The pros don't.