Webbing between molds is a very common issue. Try putting more distance between your molds. Typically you want half of the height of the mold in distance away from other objects. For example: If your mold is 2 inches tall, a 1 inch gap between the molds is ideal. If you're limited on space you may try using a manual plug assist to force the material to lay flat in between the molds. Also, feel free to experiment with mold orientation. Vacuum forming is a bit of an art, so trial and error will lead to expertise.