did you use heat N bond ---or heat N bond lite?
the regular is very heavy and not made for sewing----the lite is made to be stitched down- makes a big difference---the other stuff is made more for wallhangings items that will not be washed-
a stablizer inside the garment can help keep things from stretching or puckering- you can get tear aways or water soluble stablizers that work real well- after making sure you have the right fusable product.