This problem of flat dreads is very common with new, soft dreadlocks. They are still really just hair glued together with wax, and haven't yet started developing into the tight, matted knots that make locks. So when they are still soft, they will get squashed and fall apart sometimes. The best thing for them is just patience and backcombing to make them tighter when you have the chance. It's a pain, but worth it. The flat dreads eventually join others and fill out as they tighten up - they will not be flat forever. It's just another one of those little tests of endurance that make you so glad it's all over once they really start rocking. Don't worry about it too much, and just use enough wax to keep them stuck together in the beginning. If you want them to not be flat right away, try palm rolling them back into a tubular shape.