Keep an eye on it and see if it changes in size, shape or color. If it does, get it checked out. Otherwise, I think you can mention it to the doctor the next time you go in for her check-up.
You might consider NOT using sun block all the time - all the reports now are indicating that we have a massive problem with kids not getting enough calcium because they aren't getting enough Vitamin D to help absorb it. Vitamin D is a "freebie" from the sun so the experts are advising some sun exposure without sun block in the early or later parts of the day. Our understandable concern with skin cancer is causing other problems, like weak and broken bones, excessive injuries in sports, and so on. So, all things in moderation.