The Rams' defeat means they will be unable to match Sunderland's previous worst mark of 15 points but Jewell admitted he never really believed his side could claim the six points from two games required to beat the mark.
Rovers' player of the season Roque Santa Cruz scored twice and fellow striker Jason Roberts once as the home side recovered from the shock of the visitors taking the lead through Kenny Miller.
Jewell said: "It's not about that. It would have been nice to have got six points from our last two games but we all know on the form we've shown this season it wasn't going to happen.
"The important thing now is trying to build for next season. There has to be a whole culture change. We have to be mentally stronger as well as physically stronger and that's what we have to do between now and June 27."
Jewell pronounced himself "comfortable" with the budget he will be given to change his side's fortunes in the Championship next season but admitted it was nothing like the £12million kitty suggested in some quarters.
He added: "I've got to try to chop and change and whatever I can generate I can put back into
the players. But I'm comfortable with the budget and the amount of manoeuvring I can do."
Jewell blamed more slack defending for his side's inability to build on a bright start and hold onto Kenny Miller's surprise 19th-minute opener until half-time.
He said: "It was the same old story and it's what relegated teams do. We played well for 44 minutes but didn't concentrate. We created some decent opportunities but that goal was a kick in the teeth."
Paying tribute to 5,000 vocal travelling fans, Jewell continued: "They must be the best supporters in the country considering what they have had to watch. The sooner we can give them a team they deserve the better."
Rovers boss Mark Hughes hailed his side's second-half improvement which means they will head into their final game at Birmingham next week with an Intertoto Cup place still up for grabs.
Hughes said: "It's fantastic that we've been able to take our season right into the 38th game. We've never been out of the top 10 all season and I think for a club of our size that is a huge achievement.
"It was really important we finished the season on a high. Overall it has been a good conclusion to our home campaign and hopefully we can go to Birmingham and come away with what we need."
Hughes admitted the Rams had given his side plenty to think about in a below-par first period but praised the way his players responded to hit back and eventually win the game easily.
Hughes added: "Derby pegged us back in the first half and worked extremely hard to get themselves in front. We were possibly a little bit fortunate to go in level at the break.
"But we regrouped and came out for the second half with a lot more drive and purpose and ran out comfortable winners in the end. We had made it too difficult for ourselves in the first half."
Sporting Life