Lovely! Looks like you put a lot of work into this one!
I saw the aluminum foil trick on blog also but have not tried it out yet. it was on http://pastimesquiltdesign.blogspot.com. It was an entry in Feb.
I don't know how he did it, but recently I saw something about taking several layers of aluminum foil and cutting narrow strips of the layers. I'm thinking they had 4-5 layers. Haven't tried it yet, so I don't know if it works.
Thank you for the info, I will have a look at it hopefully it ill be ok.
Here's a thread that talks about repurposing cutting mats but it also mentions some fixes for warped cutting mats that you may can use. Hope it helps.