The Danish driver qualified 32nd on Friday, driving the #09 Phoenix Racing Chevy, with technical support from Hendrick Motorsports.
Magnussen's NASCAR deal came together thanks to his links with General Motors through the Le Mans Series, which led to testing outings on road courses with the manufacturer's top team in the Sprint Cup.
The four-time Le Mans 24 Hours class winner said he didn't get the most out of his car in qualifying, but was still happy to make the field as he had to do so on speed, given that his entry was not guaranteed a start in Sunday's race.
"We're in, which was the goal," Magnussen told AUTOSPORT. "I would love to have been a little bit further up but I was being very cautious not to make any mistakes and you only have like a third of a lap to get heat into the tyres. I didn't feel comfortable pushing like hell in the first couple of corners, so I took it easy, tried not to make any mistakes and was in [the race] safe."
Magnussen has enjoyed his first NASCAR weekend and says he would like to pursue his experience in the series further, as he feels he got little time to prepare for his debut this weekend.
In the final practice session before the race, he managed to finish tenth fastest, something he hopes to be able to back up in the race.
"I love being here," said Magnussen. "Everything about it is pretty fantastic except for the very limited time you get in the car to prepare yourself. I've never been this unprepared for anything but it was just important to be in the race and we'll work from there.
"Thirty-second on the grid is absolutely not good and we were way further down than what we were in practice earlier in the morning, but it's more important to be in the race than trying to go for something big. I'm pretty happy. I'd like to be further ahead but I'll have to do that in the race."
Magnussen carried out a test session with all four Hendrick Motorsports race drivers at the Carolina Motorsports Park in Kershaw, helping the team with his feedback in preparation for this weekend's race at Sears Point, back in April.
He says he was able to run very close to the times set by them, and expects to be able to prove that on Sunday's race.
"At the test we were very, very close," said Magnussen. "I think I will be on Sunday also, I just need more than one lap to prove it... A top-ten would be fantastic. For me I'll take whatever I get but I believe that we had a car in qualifying capable of a top-15 at least, had everything been right."
Magnussen's deal to drive for Phoenix Racing is set for this weekend only since his American Le Mans schedule clashes with the second road course event of the season at Watkins Glen in August, meaning this is likely to be his only Sprint Cup series outing of the year.
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