Mask staying infront of keyframes

[Charlotte27288580gi96]

I'm creating a transition wipe, and using the pen to make a mask. I then create all the keyframes, but as I go back before the keyframes the mask is still on the clip. How do I just make sure the mask starts when the transition is meant to start?

The picture i posted is a very quick example where you can see the black mask is before the keyframes 

[Richard M Knight]

I'm sure there are easier ways but I would keyframe mask expansion with a keyframe where you want the effect to start and another one frame earlier with the setting so the mask clears the frame.

[Charlotte27288580gi96]

So have a keyframe completely off the clip? 

[Ann Bens]

Cut the clip on the first keyframe. Remove mask for first bit.