GSC10 right? Common problem. Move it toward the rear of the left chain stain where it gets closer to the crank arm.

Tip: For a clean installation, you can stick a rare earth magnet to the inside end of your pedal spindle for cadence. I use 3x12mm magnets for this purpose. Alternatively glue the magnet to the inside of the crank arm with RTV.

Better yet, got the Garmin user forums and search and post your questions there:

https://forums.garmin.com/forumdisplay.php?f=20