Re: How concerned should I be
Yes, your chances are good since you sought treatment immediately; hopefully, you are receiving the right antibiotic and it will be administered for the proper length of time. Most non-specialist lyme docs don't understand Lyme Disease so they don't treat properly, but as I said, since you got it early.
You might, however, also consider following up with an LLMD - lyme literate medical doctor - just to make sure. Also, were you able to finally remove the last piece of the tick? If your present doc does test, make sure it is sent to Igenex Lab in Palo Alto California. You might also want to read the post at the top of this lyme board titled "lyme newbies".
It is good to hear of someone who, hopefully, will not have to go down the road of so many of us and develop chronic lyme disease. Good for you for attending to the bite early. You might also want to do some research to learn how pervasive an infection can be if not treated early by a competent MD.
All the best!