Nice job for your first attempt! A few minor points to make the system better.
First, if your chains were to break you would need to remove either your front or rear rail to access them. As of now that may not seem like a big deal, but once you have electronics and a superstructure added to your robot it will become increasingly more difficult. Take a look at the chassis on our 2014 robot, we use internal belts, and we leave the tube ends open to have access.
Secondly, have you considered using gusset plates on the top of your rails to connect them instead of the aluminum angle? You could use VEX pro parts, or make your own. You could just match drill them if you do not have access to a mill. I think that a gusset plate and rivets will create a stronger connection than the angle in the corners.
I hope this helps!