If you have sanded down to the nail heads, you can fix this, although with a lot of work... You take a punch and hammer and give every nail a beating

You'll feel every vertebra for at least a week, but by driving the nails a bit further in, you gain a bit more ''flesh'' for future sanding, afterwards you take the sanding dust, mix it with wood glue and fill the holes.

The same procedure like on long board wooden floors indoors.

Incredible amount of work, but way better than ugly iron stains or a nail ripping a nice groove in your bare feet (and now nice blood stains in the wood) ;-)

Check from time to time if nails work themselves up, wood is constantly ''working'', so nails tend to come out over time, if they become loose, pull them, put matches with wood glue in the hole and hammer the nail back in.

Or you go completely for larch or Douglas fir for your next deck, those don't have to be sanded/stained, as long as the underconstruction is well made, so the wood can dry completely, the wood gets grey but doesn't rot. Such decks can last up to 100years if done properly (proper ventilation, groves between the boards, not mounted directly on concrete, no always shady places, nails/screws out of stainless steel).