I had the same issue in the pool at first. Then I told the instructor (before next dive) that I was not comfortable as I was trying to rush through and that on my next attempt I will just take it off, do few breaths w/o mask and then put it on and clear. He was ok with it and that is what I did.
I found out that if you do not rush things it is much easier. (Obviously you need to find your regulator ASAP and stick it in your mouth, purge and breath, but mask can wait
Slow and easy wins the race for me.
I do at least partial mask clearing on EVERY dive so far (at 34 dives since June of this year now).