With the bed warm, I peeled it back. I should've had wax paper handy so it doesn't restick when you let up on the pulling even for a second. I peeled from each corner inward, as a straight across pull was talking a lot of effort. Then I cleaned the surface with GooGone. And used a straight razor held really flat to scrape off the glue while it was soft from the GooGone. What a job, took quite a long time.
I emailed 3M, who makes the mat, asking if they had tips for next time. They said they don't have something specific if I don't have the 3M product number but this is what they sent (#8 is toxic chemicals):

There are eight methods that can be tried for adhesive removal:
1) Soaking the area liberally with water may soften the adhesive if it was put on the surface within a day or two. The adhesive will turn white and become stringy and fairly easy to remove. (You may need to keep a sponge or wet towel over the area, to prevent the water from evaporating during the 24-48 hour period.)
If the tape has been on the surface for long periods of time and, or, exposed to sunlight, and heat, first try peanut oil (see Item #2 below).
2) Put some peanut oil on a soft cloth and rub over the adhesive area; let it soak for a few minutes. The oil will lay down a film alongside the adhesive, so that when the adhesive moves it will not re-adhere to that area. In addition, the area of adhesive exposed to the oil will become de-tackified. Keep rubbing in a circular motion until the adhesive rolls up into a ball for removal. Follow up with soap and water to remove the oily residue.
3) A concentrated citrus solvent like "Goo Gone", available at most Department, Hardware, and Grocery Stores, has been known to work for removing adhesives also. Follow the same procedure as the peanut oil.
4) To remove adhesive from a washable surface: Cover adhesive with a cloth or sponge saturated with warm vinegar and let stand. When the adhesive is saturated, it may peel off without scraping or causing damage. Rinse. (Note: Use this method only on washable surfaces and washable paint.)
5) Hand cleaners like DL, Fast Orange, GoJo, or Goop, usually in an auto department, can be effective in softening and removing adhesives. . Spread them on, wait 10-20 minutes. Wipe away any softened adhesive; carefully scrape surface with a hard plastic sraper, or flat piece of wood. Repeat, if necessary.
6) Adhesive and paint removers, such as "Goof Off" and "Oops", can soften many adhesives. However, these materials are flammable, have health issues, and can damage certain surfaces; it is the customer's responsibility to read and follow all directions and precautions, and to determine if these materials will damage their particular surface.
7) Heptane, toluene, and MEK (methyl ethyl ketone) are solvents that will soften some adhesives into a soft, gooey state and, by continually rubbing over the area, the adhesive will ball up and can be removed. However, the solvent could damage your surface; test in an inconspicuous area to assess whether this method is satisfactory, before proceeding. These solvents are flammable and have associated health issues; the customer is responsible for reading and following all directions and precautions.
8) Some adhesives will not respond to any of the above methods, in which case you may have to resort to using a razor-blade scraper. However, the razor-blade scraper could damage your surface; test in an inconspicuous area to assess whether this method is satisfactory, before proceeding.
To accomplish adhesive removal and minimize damage to painted surfaces, it is recommended that the least aggressive compounds are tested against the residue in an inconspicuous area. The mechanics of adhesive removal dictate that the adhesive must be "softened" to the point where it may be lifted from the surface. For that reason, it is recommended that a very loose weave cloth be used in lieu of paper toweling. The reason for this is that the adhesive can "imbed" itself into the "nap" or weave of the cloth verses "smearing" it around on the surface when attempting to use paper toweling. Cheesecloth is excellent for this purpose.
I have also found that WD-40 works well to remove adhesive residue."