Molding Plexiglas into a slight bowl shape?

Hi DIY, I'm trying to mold a snall piece of Plexiglas into a slight concave shape. It's for part of a cosplay mask I'm making for somebody. Would anybody know what the best way to do this would be? I've tried using a heat gun to make it pliable but it doesn't seem to heat up uniformly. Would I be able to use an oven? I only need to curve it a little bit just to make it slightly round. Thanks!