Monday night's 24-9 loss saw the Rams fail to capitalise on several touchdown opportunities, with McVay pointing to "self-inflicted wounds".
San Francisco's Deebo Manuel caught six passes for 115 yards and a highlight-reel touchdown, and when the Rams were still in the game, at 17-9 in arrears, quarterback Matthew Stafford was intercepted by Talanoa Hufanga. That pick-six summed up the Rams' night.
"I liked the way our guys battled, they competed and got it to a one-possession game," said McVay.
"But the story of the night from an offensive perspective was self-inflicted wounds, above-the-neck errors where we're not doing things we're capable of, and I expect us to be better than that.
"Defensively, I know we continue to battle, we gave ourselves a chance. We can tackle better, you credit them for making the plays, and I thought special teams hung tough, but overall we didn't do enough to win the football game.
"I'm not going to make any excuses. We've got to play better. A lot of it was just things where guys we were counting on didn't do what they were supposed to do."
McVay took his share of the blame, saying: "I put us in some bad spots.
"However you want to cut it, we have to be better collectively, coaches and players. There's no other way around it and no way I know how to fix it other than go back to work."
The Rams will face the Dallas Cowboys, who are on a three-game winning streak, in Week 5.
"Everybody needs to be able to look inward," said McVay. "In the red area, to have three good drives and only come away with nine points in a game that was a back-and-forth battle like that, that ended up being the difference.
"And when you do make it a one-possession game and you've got some momentum, a couple of game first downs and we throw an interception for a touchdown on a screen, those are the things that don't help you win games."