The ornamental design for a gymtowel, as shown and described.
FIG. 1 is a front perspective view of a gym towel showing my new design;
FIG. 2 is a top view of a gym towel;
FIG. 3 is a bottom view of a gym towel;
FIG. 4 is a right side view of a gym towel;
FIG. 5 is a front view of a gym towel;
FIG. 6 is a back view of a gym towel; and,
FIG. 7 is a perspective view of a gym towel showing it in use on gym equipment.
Left side views not shown are mirror images of right side views. The gym equipment in broken lines in FIG. 7 is environmental subject matter that forms no part of the claimed design. All other broken lines depict stitching.