Magnussen and Hamilton collided at Turn 4 on the opening lap of the race, with the contact giving both drivers' cars a tyre puncture.
Magnussen's radio message after the clash suggested he felt Hamilton had intentionally forced him off the track.
The Spanish GP stewards decided the collision was a racing incident and did not penalise either driver.
When he spoke to the media after the race in Barcelona, Magnussen had still not seen replays of the incident so did not want to comment further on it.
On Thursday, speaking ahead of Sunday's Monaco Grand Prix, the Danish driver said he had rewatched the collision and accepted that his initial feeling had been incorrect.
"Yeah, I had a chance to look at it and of course changed my view on it," Magnussen said. "I had a feeling when I was on the track that he opened his steering, but that's not what happened.
"He got into the slipstream of the Ferrari, understeered a tiny bit. I was super close to him, and I gave him [not] much room for error, gave no margin."
He added: "I just wish I had turned in one millisecond later to have a little bit more... in a corner like that, if you're gonna go round the outside, you want to be as close to him as possible.
"You don't want to go too wide and into the dirty part of the track. That's what I did. We touched, unfortunately."
While Hamilton drove through the field from 19th back to fifth and was voted driver of the day, Magnussen failed to convert what had been a very strong qualifying performance into a single point for Haas.
"There was also a lot of bad luck," Magnussen said. "If I had been a little bit further forward when we hit, we would have hit rim to rim and it would have been different. But unfortunately I just hit the side of the tyre on his side of the tyre, puncture.
"Wish I had given him slightly more room."
The Monaco Grand Prix is live on ESPN at 8.55AM (Eastern Time) on May 29.