Mimic line tracker issues

For my first Mimic project, I tried to add a line follower sensor to the example Tank Drive mimic. Here is my project. It has a couple issues. One is that the the sensor is not properly held down, and it swings around when driving. I tried to secure it with a screw, but as you can see, that screw is just suspended in the air now. I have no idea why. Another problem is that the line follower does not actually work. The value it returns seems completely constant regardless of whether the robot is above a light or dark part of the floor. I’ve tried flipping it upside-down, but that seems to make no difference. I know it’s probably in the interest of performance, but the overly simplistic graphics don’t help this problem, since I have no way of telling one side from the other. Hopefully somebody can help me get this working.