My always failing middlegames: FIDE Junior Invitational Round 1

I played in the FIDE Junior Invitational in the Seattle Chess Club during the weekend (March 11-13). I came in as the sixth seed, with 7th being only being 4 points behind me in rating. My goal in this event was to get a plus score, because that would be a good performance. In the end, I achieved my goal.

During the tournament a Kings vs. Princes match was held, and the Kings won in the end, by winning most of the rounds and having much higher (nearly 100 points!) ratings.

On Friday night, starting at 8pm, I was scheduled to play Jacob Mayer, rated 1755, slightly higher than my 1743. I was black.

Opening 

I decided to give the French a try, and my opponent played the French Exchange.

Middlegame

At this point in the game, I was unsure of what to do. I needed to come up with a plan, something that in many games I don't do, even though that doesn't make sense. I considered whether Nf5 might be a threat or not. In the end, I decided I wanted to develop my queenside knight, Queen to d7 and put a rook on the e file. I managed to get this. 

Despite this horrible middlegame by both sides, with my opponent winning at several points, I lucked out at the end. 
I'm not sure what I can do to improve my middlegame skills. It seems that in nearly every game against players 1500+ I am nearly losing or losing in the middlegame. That is pretty bad. But at least I luck out later, in the...

Endgame

The Endgame kicks off with a huge blunder by Jacob, and many later to follow:

So that is my lucky round 1 win in the invitational. I'll post the other games sometime... when I have the time!

Feel free to leave comments, questions, and advice on how I should improve...

Thanks for reading!