I am trying to sewing a piece of muslin to my bicycle shirt to create a pocket for inserting a shoulder pad. Strangely, the top and the bottom threads did not catch each other. Is it because the quick-dry material in my bicycle shirt made of much more spandex and synthetic materials, which do not go along with cotton??? The quick dry-shirt looks very ugly with bigger needle holes, compared with the muslin, after my attempt to sew them together. The quick-dry material almost looks like not woven.

Anyway, how can I solve this problem, and successfully sew a pocket to the quick-dry shirt? Thanks