do you mean the embroidery waves in areas? like it doesn't lay flat? Are you over stretching when hooping the material? T-shirt material isn't the best for embroidery. It's light, stretchy and will shrink when washed but the embroidery wont shrink with it leaving a wavy look. A stronger backing works but it does depend on the embroidery. Does it have open areas? and does it have the proper underlay? I would try embroidering on a different material then wash it. If it doesn't bubble or wave then you know its the material not the design.