The second slack-throw is a little strange. It's almost like a totally different move than the first throw. It seems a lot harder than the first one when you're first learning it (at least, it did for me), but, once you get the hang of it, it's a snap.
Also, quite a few of the moves in this trick are just overall awkward at first. There's so much arm-crossing and hopping and stuff. Just keep working on it and it may just become one of your favorite tricks to do!