Oops, I messed up.

[CaptainSEO]

I started a traditional slat, sugar and saltpetre cure on a belly of pork last Friday (3 days ago), however, I just realised I forgot the saltpetre.

Is it ruined? should I unwrap it and add the saltpetre now?

[ComradeQ]

I would add the cure now and just add a few more days onto the curing process. As it has been under refrigeration with the salt and sugar there is no risk that the meat is spoiled. There are many who don't even use cures (I feel that it is too risky not too, also the flavour will be more like roast pork and not bacon) so you should use it for sure.

[Big Guy]

Yes just add the cure and start the clock from zero on your curing time. We have all been there.