You swing looks nice. If you want to increase your serve power to the max with limited space. It looked like you tossed for a floater. Add some topspin to the serve next time, it will make it so the ball will start to fall on the other side of court. Make sure the last step of the approach is slanted, look up spike approach on YouTube to see what I'm talking about. This footwork will make it so you are traveling upwards instead of forwards. Another thing is to counter balance your swing, you can do this by kicking both of your legs back while you are in the air. It makes it so you can hit harder due to the nature of momentum when swinging. Adding a few inches to the ol vert will enhance all of these adjustments too!