Hammer-ons are a great tool to help you get more notes with out giving too much of the workload to your picking hand. Practice landing right on your finger tip to get good volume. Watch your timing in the B part. Use the app when you are away from the instrument to listen to the timing. Isolate the measures with the dotted 8th and quarter notes separately. Listen to the measures repeatedly until you can hum along with the mandolin. If you are on your computer, go to "more settings" in the bottom right hand corner and dial down the band volume so you hear more of the mandolin. Listening is just as important to your musical development as playing your instrument.