Yes, Gordon. I bought that exact kit a few months ago and, as it happens, the comma dolly is what made those marks!
(I drilled a divot into one side to cup (and not deform so much) those big round rivet heads whilst I smashed the other ends of them with the planishing hammer. Then I held it too tight and too flat against my formerly clean aluminum skin, resulting in those mars).
The other "real" rivets I have for this project are much smaller and flat-headed—both more like what the original Spyders actually had AND easier to set without a proper rivet tool. I won't need to do too many more. I think.