it's the outer edge key of a keyboard that's placed in a backpack, of course it's user error... something happened, if it was the "F" key... sure that leaves more to the imagination, but not the outermost key.
you have another ctrl key on the keyboard, so i'm guessing you're already using that, there really is no or limited options, it's to:
live with it,
superglue the stem on and hope it doesn't break off, i recommend gorilla glue
re-learn how to solder again
RMA really isn't any company's fault but your own... i mean if it came shipped like that, sure but not after use, especially when it's been put in a backpack.