Did you have prepaired the clothes in DAZ3D yourself, or is the duf something from an other source? If you prepared the cloth yourself in DAZ and have fitted it correctly to the standard genesis 2 female in the right size, this should not have happened. Looks like this step maybe was left out.
If you did everything corretly in DAZ like described in the tutorials: Sometimes, if you try to fit an mesh edited with a 3rd party tool (like Blender e.g.), only resizeing and lining it up in DAZ isn't enough. Your changes will not be permanent. Try to unparenting you mesh in DAZ and to delete the Genesis Figure... does your mesh stay in size and in position? Did you try to save and re-load it in DAZ and does it stay in shape? No? Sometimes just a simple trick will help: exporting it as OBJ and re-importing it in DAZ. but don't forget to re-assign the textures in DAZ from a proper source. The materials included with the OBJ will not work correctly when importing in VaM. If nothing helps and it won't keep in shape, then try to convert the cloth item to a proper DAZ-geometry using the options you find in DAZ: Edit/Object/... This is not trivial to explain, so please look out for that point in the tutorials.