I've just started to begin to do the frog stand, but I've been having some problems with it; first, I think I feel too much pression/sort-of pain in my knees, because they are the ones who basically sustain me there, and second, I also recorded myself trying it, and I can't seem to put my back straight like the kid in the pictures, instead it's too arched, and I either bend my arms too much, or go forwards too much, so I'm pretty close to the ground.
Any pointers with this? Thanks in advance.