Nice video, excellent serve. You have some nice ground strokes as well. It looks like you make the same mistakes I make, so maybe you will find this useful.
First, I think your poor net play was just taking your eye off the ball a little too soon. Second mistake is when you hit a hard groundstroke and just watch it instead of preparing for a weak return, I do this sometimes thinking I hit a clean winner. I forget that not everyone is as slow as me.
The third mistake (I hope someone else reading can chime in) is watching the ball instead of the opponents racquet. You seem to be caught off guard quite a bit when your opponent was chipping it back instead of hitting topspin, which led to you being out of position. I think if you were more in tune to his racquet you would have anticipated better the type of shot he was going to play and would have easily put away some of those slices and lobs.