Di,
If you just purchased the mat, take it back. It is a defective product. Warping usually happens when the mat has been exposed to heat (the sun or iron).
If you think you warped it (sun or heat), iron your table surface, quickly place the mat atop and then stack heavy books in an attempt to straighten.
The mats will also crack if exposed to extreme cold. Sorry you having this problem as a newbie, but hang in there. Blessings. Suz