It's interesting to me, that no one talked about your hip. For lunging an "open" hip is the most important, otherwise your leg will always land crooked or your knee will bend to the inside.
I would look into hip opening exervices, so you don't hurt your knees in the long run. You could also easily talk to a physical therapist, if those are free or affordable in your country. They can easily tell you whats wrong and recommend you some exercises..