When signing with your baby it’s important to acknowledge your baby’s development and thus their physical limitations. Baby’s are born without much muscular coordination. With time and practice they earn the ability to move their bodies as they desire.
In the beginning certain signs/movements are difficult for a baby to do. For example twisting the hand for APPLE might appear as just the fist or hand to the mouth. When doing the sign for DAD, the thumb might not protrude and the sign for CAT might not have the outward motion of the finger tips drawn out but rather might have both hands placed on the cheeks. Baby’s find movement, especially complicated ones, difficult to do. The sign for BEAR which involves crossing the arms over the chest with fingers clawing (opening and closing) might just appear as one hand clawing absent of arm crossing. Babies find crossing their arms difficult to do at first.
Consider too that when you model signs that your baby is seeing the mirror image of your example. That means that your baby might do the opposite motion and movement as they attempt to replicate what they have seen. The precise location of the sign also often suffers. Hands might touch the side of the head instead of the forehead, a finger might touch the edge of the nose instead of the mouth and so forth.
None of these “mistakes” should be of any concern. These are just your baby’s way of working through their signing vocabulary and “sounding” out their words. With time, the signs will become more refined so long as you continue to show them the right way to do them.