Place a piece of plywood over top of your acrylic. Clamp your acrylic and plywood sandwich to your work bench such that 1" of acrylic is sticking over the edge (and no plywood is). Measure carefully on both corners of your material to make certain that 1" is truly hanging over.
Heat up the 1" strip of acrylic with your heat gun, by moving it back and forth along its surface until it visibly starts to droop. The acrylic is now very hot. Put on your oven mitts and bend the acrylic down towards the floor to a 90 degree angle and hold it in place until it starts to cool and maintain this shape on its own. Let go and wait a few more minutes for it to cool more.