I had a slightly sunken nipple which the doc said was nothing to be concerned about. Later a routine mammogram detected a very tiny lump which has been removed and I'm now clear. I know it's worrying but it's good to make sure and if it is something to be concerned about you will have caught it before it gets out of hand. As everyone on here knows - waiting is the worse part of the whole process.
It's no good saying not to worry as of course you're going to worry but you would have still worried even if you hadn't shown it to the doctor. This whole cancer thing doesn't have to be traumatic - mine wasn't and I hope you are even more fortunate than me.