If you can get to a pool, that's what you need to do. You should not have to blow "hard" at all into your mask to clear it, all you'll need is a bit of pressure to displace the water.
When I first started AW classes I had some trouble with mask clearing. I was fine when all I had to do was stand and put my head under water while holding my breath, and clear the mask, but for some reason, when breathing off the reg was added to the issue, I had trouble doing both at the same time, and had an almost overwhelming urge to bolt up to the surface for air. This is how I fixed the problem. It may not work for you, but here it is for the info.
I would go to the shallow end of the pool, and first put the reg in my mouth with out a mask on, and practiced breathing off the reg under water. Then I put on the mask without surfacing, with water in it, and breathed again for a while, with out clearing. That was a bit harder for me for some silly reason. I guess it's like rubbing your belly, and patting your head kinda thing.
After I got comfortable with breathing and having the mask full of water, I tried to blow a bit out through my nose, and clear my mask, while still takng breaths. I did that over and over again, until I felt comfortable doing it, then I moved into deeper water and did it all over again.
That was in 1976, and to this day I still feel a bit funny, breathing while my eyes are under water, but I can clear my mask any time now without problems, almost without thinking. Now clearing is easy, it just takes time and practice, without someone pushing, or watching you, so you can go at your own pace. Good luck