It can’t be ignored. Like the clacking of rat toenails on wet pavement or a ghost’s breath upon your neck, Submitter’s Regret is a dastardly thing that can drive you insane if you let it.
There are always things that you’d wished you’d done better. Or different. Or not done at all. Or not done as much.
Acknowledge these “should haves” only briefly, then dump all on the backburner and look quickly away.
There is nothing to be done about them now. Later, perhaps, they will teach. But at the moment they can only torture.