So, you are in a time bind. Avoid that if you can. I cut some of my mats and buy some already cut. I prefer the Bainbridge Archival Museum Quality Mat and generally get them from Iconusa.com if I'm going to buy them. I use self adhesive Linen Hinging Tape made by Lineco. I hinge the top of the mat to the back board and then use a pendant mount for the print. Although I use to dry mount my prints, I doubt I'll ever use that method again. The method I've described is very forgiving and is (in my opinion) a less damaging way of mounting. Should the mat get damaged, the print may be salvaged this way, but couldn't with a dry mount. My 2 cents worth. Bill Barber