Borthwick has lost six of his nine matches in charge since replacing Eddie Jones (63) in December, including five of the last six.
Fiji's 30-22 win at Twickenham last month was the Pacific Islanders' first ever over England in a final warm-up game for Borthwick's men before they take on Argentina in Marseille on Saturday.
"We've been through a pretty turbulent time but I sense it has made us stronger," Borthwick told the BBC.
"I sense for us there is a renewed determination. And I certainly get the feeling from the players that they feel they have been written off a bit too early.
"There is a feeling people have rung time on these players. And I think that decision may have been made a little bit too early."
England will be without suspended captain Owen Farrell (31) and Billy Vunipola (30) against the Pumas, while starting scrum half Jack van Poortvliet (22) and wing Anthony Watson (29) have been ruled out of the tournament due to injury.
But Borthwick otherwise has 31 players to choose from and remains confident his side will come good when it matters most.
"We have been building towards 9 September and being ready for 9 September, and that has not changed," he added.
"We know it's a formidable challenge, but I look at my players and I know they like a challenge.
"They have been challenged both on the field and off the field, but they are up for it."
Farrell said on Monday he is "gutted" to not be able to lead his country in the opening two games of the World Cup, but has accepted the red card that led to his controversial ban.
He was sent off for a high tackle on Wales' Taine Basham on August 12.
His red card was initially downgraded to a yellow by a disciplinary hearing, only for World Rugby to successfully appeal the decision after a widespread outcry.
Farrell's four-week ban means he will also miss England's second pool game against Japan.
"I made a mistake and I got banned for it in the end. I'm not going to sit here and moan about it now," Farrell said.
"I'm excited for this World Cup to start. I'm excited to see what this team can do and I look forward to being available again.
"I'm gutted not to be playing and I'm gutted not to be available. Especially a big game like this at the weekend."
Despite their poor form, England's prospects in France could be aided by a kind draw.
Farrell should make his return against Chile before England take on Samoa in their final pool game.
"I'm excited for the team now," added Farrell.
"There's a real good feeling about the World Cup starting in France now. I'm excited to play my role in that."
