Any tips on flattening a photo in a frame?

I made a 20x30 print and framed it. I have tried a half dozen times but can't quite get it totally flat. Any ideas? It is a cool picture but it looks kind of cheesy with the "rolls"

Thanks

When I have a rolled print I want to frame, the first thing I do is flatten it out before I frame it. I start by unrolling it and then rerolling it the opposite way that it was originally rolled. Then I unroll it and lay it flat on a table and then set something on it. I will leave it like that for a day or two, longer if I have the time.

When it comes to framing it, I attach the print to foam core board. I use the hinge method to mount the print to the foam core. Basically I'm only attaching the top of the print to the foam core in 2 spots at the top, so the print is hanging. Then I lay the matte over the top of the print, and the matte holds the edged down to keep it from rolling.

Thanks for the tips Mike