My guess is that the default sitting animation is being played on top of your custom animation. The default sitting animation raises the legs to a 90 degree angle, and since your custom animation raises the legs forward slightly, it seems plausible (to me) that this is what’s going on.
I have no experience with doing this, myself, but you can try reading this forum post and see if it helps you. If not, I’d suggest looking up “removing default sitting animation” or something similar to that in the Dev Forum.
I may be a little late, but previously, have you added keyframes in all body parts? By default Roblox animations are set to Core priority, and anything with a higher priority should overrun it.
I’ve ran into this problem before and I found out that a part has not been animated (judging from your picture, it could be the upper leg/ lower torso). This allows the default animation to take its place and play instead.