Dee you're doing a great job! When you are doing round 2 on your squares (and every round after) you only need to work your stitches in the spaces, not in the actual stitches from the previous round. Also, you are doing 3 chains in between all groups there and you only need to make the chain 3 for the corners If you're still confused, I can do another video of the square from the beginning!
Love your pet mat! Make sure you are counting your stitches because I have had issues where my piece slowly narrows because I am leaving out stitches in my rows