The Scots have headed to Auckland for their pool decider with England on the back of their 13-12 loss to the Pumas - with Lucas Amorosino scoring the decisive late try in Wellington.
Scotland must now beat England and deny them a bonus point if they are to continue their proud record of reaching the knockout stages of every World Cup.
However Parks claims the loss to Argentina has had a massive impact on the squad.
Parks said: "It's very hard to accept losing that game, but we have to, because it's done. We've got to move on.
"It's the most heart-breaking thing I've been through, rugby-wise.
"Someone asked me about looking forward to England. It's really hard to look beyond this one, but the reality is you have to.
"It's still heavily weighing on the mind.
"The hardest thing to accept is it was on the biggest stage and it was the most important game we've had for a very long time.
"We've had discussions and there is obviously still hope we can still get through."
Despite the agony, Parks insists Scotland can regroup and pull out a result against the auld enemy.
He added: "We are capable of pulling out big results and there's going to be none bigger than this week.
"We've proved we can win games and that (against Argentina) was a game we know we should have won.
"It's a very, very tough thing to take because it was all set up for a big finish. It was just one of those things. It possibly wasn't meant to be."
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