Vern Cotter’s side overturned a second-half fightback by Ireland to win 27-22 on Saturday and open the championship with victory for the first time in 11 years.
Success over an Ireland side victorious against South Africa, Australia and New Zealand within the previous seven months has boosted Scotland’s confidence ahead of Sunday’s match in France.
However, Fagerson was keen to point out that Scotland will not get carried away.
The hosts were under the cosh for much of the second half at BT Murrayfield until two late Greig Laidlaw penalties got them over the line.
The Glasgow player said: “We’ll look back at the tape and see what we did well and what we didn’t. We’ll also have to see what threats France will pose us. I think Saturday’s result will give us a lot of confidence – but we can’t get ahead of ourselves. It’s only one game.
“It wasn’t an 80-minute performance. We switched off a few times and they came back into it. We made it difficult for ourselves.
“If we can get an 80-minute performance and stick in like we did against Ireland we can go over there and get a result.
“It was a great result and we’ll take the benefits from it. But we weren’t perfect.
“We made a hell of a lot of errors so if we want to be the best team, we need to scrub them out and put in an 80-minute performance.
“Once we can do that, I’ll say we’re on the way.”
Fagerson made his Scotland debut a year ago and admits he feels more comfortable in the set-up – but not “at ease”, as he was asked.
“To be brutally honest, I was absolutely burst at full-time,” the 21-year-old said.
“I wouldn’t say I’m at ease because you can never relax in Test rugby.
“There are always new opponents coming in, so every week changes.
“You need to be on your toes all the time.
“I’d say I’m more comfortable than last year. I was pretty chuffed to start and felt I did okay. Not comfortable but a bit more relaxed than last year.”
Fagerson has also noticed an improvement in the entire squad ahead of Vern Cotter’s final Six Nations in charge.
“We’ve had a lot of confidence in camp during the week,” he said.
“We got a lot of depth coming through and training has been at a real high standard. That’s been spurring the whole team on.
“Training has gone up another level, so I think that was transferred into Saturday’s performance.
“In the first half, we were pretty clinical, especially with the backs. They were pretty good, the forwards weren’t at their best.”