yup you probably missed something at the store. btw, always store in a microfibre bag before storing in any cases. its a 'just in case thing' ....but i forgot once, and the knot from the string on my microfibre bag actually wore away a spot of iridium on my livestrong radar lens.
Does the dent possibly look like a small bubble in the lens? If it does it could be a lens defect which is very common in all the lenses. Sometimes they end up in the vault because of this. Then if so its under warranty....