I wouldn't even bother with trying to recut it. You will not get it right. And bying a spi is by no means as expensive as a few years ago.

Or what you can do it lend a spi from a buddy which you think is good and lay it flat on teh floor, measure it and try to make your panels the same shape and sew it back together.

Apart from that, buy a new one and reck the oldy in a blow while having major fun with your best mate.

Wouter