Nice first tries.
By "omitting", Concerto means you just have to "cut" or "delete" the part you don't want to appear onyour layers.
To know where to cut, just download the original map (the one with all the "squares") on the charcater before you add color on it. It will help adjusting the shape you wish to reach.
So for example, to make a T-shirt from your pull over, you'd just need to cut out (delete) the lower arm part on your layers. Or to make a "V" collar, delete some parts around the original collar. And so on...
Have fun and keep on!