Here's what I used to do when I was DM'ing for an instructor and he had me work with people having trouble with this skill.
Flood your mask about a half inch up and breath normally for 3-4 breaths. Then flood it up about half way and breath normally for as many breaths as it takes to get used to it. Then flood your mask almost all the way or all the way and leave it on and breath normal. Open your eyes with the mask on if you closed them and continue to breath until your breathing smooths out and you relax. Then pull the mask away and off your face and you will notice there is no difference between breathing with a full mask on your face and no mask. If you freak, don't go up, instead close your eyes and plug your nose and concentrate on breathing normal and calming down. Once you've calmed down, open your eyes and breath several times then let go of your nose and continue to breath. Once you can do this sit underwater with no mask for 10 to 15 minutes and just breath.
As you flood and take off your mask doing this incremental technique you will be able to eventually rip your mask off all at once without stopping breathing and or freaking out.
Shooting up from depth because of a dislodged or lost mask can be fatal, so this skill is critical.
If you can't master this skill, unfortunately I have to tell you, you have no business diving in open water until you get it down.
But truthfully I have never had anyone not get it using this technique, so hang in there.
Good luck and let us know how you're doing.