I’ve been trying to grow Pawpaw in zone2b climate

That's gonna be a challenge. Most of the time I see zone 4 listed as the coldest zone they can survive. You may want to look at some of the techniques people use for overwintering citrus in cold climates to try and keep your saplings alive.

Also if you haven't already you might want to look into service berries as a fruit tree you could grow in your climate. Some species are hearty to zone 2, so with your 2b zone they should be happy in your climate.