Sounds like you might just have to keep working and practicing! The muscles might be tight or simply unused to the movement, and are trying hard to get back to somewhere that's comfortable.
You can always see about getting your legs into the right position on the ground (though, be careful not to do both at the same time, as if you're tight or your knees are a little weaker, this can be very difficult) and see if you can figure out what kind of feeling you're going for.
You could also try working on one leg at a time, till you can do both. So, doing your hooked leg first, and letting the back leg just swing out back instead of trying to bend it into shape. And then, once you have that, you could work on the back leg. That way, your brain isn't trying to do too much.
Takes practice! Not all moves come easily to everyone, and sometimes, some moves just don't work for us. Just keep at it, and you'll figure out if it's for you or not ;)