not bad mate,i'd just say work on getting maximum range with your jab and twist a bit more with the back hand also think of literally breaking it as you hit it rather than pushing/punching behind the bag.

also you as has been said you were dropping your hands as the punches came back (while you were still in range)

it was a little bit frenzied; get in range get your combo off get out of range then steady the bag,

not bad though i think some partner work would help you a lot