this step is the hardest because i can not help you. your back stop will be differant from mine cause you didnt not build it in my storage room (possible great place to build one if you have one long and narrow mines 30 feet long theirs about 10 feet behind the back stop you cant see in most photos )
this is hard to exsplane so look at the pictures if you get confused
1now you want to have the blanket run from the top of celling down but not to the ground
2 you what to have the blank cover the sides.
3have the end of the blanket bank up
4it the part that slops up has to be kinda forward to so that it catches the ones that fall