Ironing out canvas ridges?
 

I have a large canvas I have painted, but it's a loser so I was going to trash it after using it to just do a study. My kids want it for their room though and that's ok.

It's a commercial cotton duck canvas, been on the stretcher bars for who-knows-how long. I want to remove it and staple it to the wall. Is there a way to get those ridges out where it wraps around the bars? I'd like to keep the extra canvas on there.

Thanks!