Needing help fixing the prone animation on my character

I am very new to Unity and am learning things very slowly through just messing around with things. But I have a new main avatar I want to use and I tried to replace the prone animation from a sitting down legs crossed to a laying down animation. I figured out how to change it but now in vrc when I prone and lay there if I keep my head still it looks normal but then the second I move my mouse just testing it on desktop the legs bend in a weird way. I do not really understand most terms for unity and things like that so if you know what is happening could you explain it like you are talking to an infant because I am so lost right now.