If it is a light weight terry, I would use a good quality tear away on the back and one sheet of washaway on top. If it is a deep pile terry, you may want to use two layers on top if your washaway is light weight. The top stabilizer holds down the pile so that the embroidery stitches lay flat. Also, a design that has an underlayment (stitches that zig zag the design before the design is embroidered) helps the hold everything flat. You can also press the design area flat before embroidery - sometimes that helps - but not enough to eliminate a topper.
If the design has a lot of coverage with the stitches, you could also use a Heataway that tears. Then you just tear the visable topper off and just leave the covered topper in (because you will not see it and it will eventually disappear in the dryer!!).