If you have any concerns about braking parts, check it out. They're all that's keeping you from sailing through a stop sign, out in front of that oncoming truck.

I would be concerned that there may be a groove on the rotor's backside that is deep and sharp enough to act as a stress concentrator, possibly leading to failure of the rotor. Unless you feel competent to inspect and judge this, a brake shop should offer to take a look at no charge, but if they see even minor damage, they'll be very insistent that you replace the rotor.
--
Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar MGB, and numerous old motorcycles)

You might have a circumferential gouge in the rotor. I wouldn't worry about it...
[Any rock that could fit between dust shield and rotor couldn't be "that" big, and I doubt that the gouge will be too deep (but it depends on the material -- some minerals are harder than others, and possibilities are from no gouge to a really deep one).]
...But, if you're going to lose sleep over this, crawl under and try to see any damage with a flashlight. Then you'll know, bad news or good.

Eventually, your pads will wear to fill the gouge, so that shouldn't be serious, but the worst case (and most unlikely) is a gouge that's deep enough to thin the rotor below minimum permitted thickness.

Good luck.