How long you learn ASL in songs? If not long, give it a time and practice. You doing a good job so far, but yet, more you practice and even in mirror if you look yourself if you understand as of testing. Yes, expression is the key and signing must follow the rythym. Not sure, I have noticed that there are lot of words in the song, but you didn't sign or you just sign on the chorus part. Not so sure. Smile.
