Have I ruined my tattoo?

If there are no signs of infection you probably are fine. You stated "it's healing very nicely so far" so most likely you will be fine. At worst the tattoo may be slightly faded from over scrubbing, but a touch-up after healed could rectify that. Perhaps give the tattoo artist a call and clarify directions of aftercare--also ask about getting a touch-up in a month based on how it looks. Sometimes the artist will do it at little or no cost if they liked you and you tipped them well. Good luck hope this helps.