Thanks! Yes, you are very close to solving it. Don't worry, because that "puzzle" is a bit misleading on purpose for reasons that will be apparent in the full game (although maybe it could be communicated in a better way to the player). As a clue, think that you are doing the reverse of decryption (so, what needs to be decrypted with displacement +7 is not the original text, but your encrypted version).
Also, it would be very helpful if you could complete the survey including this feedback :)