I would use AA batteries, they last a lot longer than 9Vs. Get a 10 AA battery box wired up instead of 9Vs for the motors, but keep a 9V for the Arduino (seperate batteries is better in my experience) and make SURE you have a common ground. That should improve run time. Use rechargeable AAs. Hope this helps.
While I can see the points people are making on both sides of this (arguement?) thread, I will point out that as a beginner, you WILL make mistakes. I've been there. So just just chill. There is such a thing as too much constructive criticism!

I like your robot.
