Cadence sensor won't fit!

Hi all,

I just got an Edge 830 sensor bundle. When i went to install the cadence sensor, i found that it won't between the crank arm and the frame on my Trek Checkpoint. No position on the inside of the crank arm will fit. I guess i could put it on the outside of the crank arm, but that will surely be annoying and I'll eventually kick it off. Any other creative ideas? Bummer :/

Also, my speed sensor arrived with a dead battery, but that's not the end of the world.