Spider-Man: No Way Home (Now all webbed up with SPOILERS)

I know that we wouldn't have a movie if he did this but why didn't Strange just shut the spell down and start over with the changes Peter wants? So the movie's events are really his fault for knowing better and seemingly not caring because he thought he was good enough to do it anyway.
Maybe some of behaviour we saw when he was a surgeon. Only wanting the interesting cases, to show his superiority... but at the same time not taking on the longshots to avoid having to face failure. He took on a very complex, delicate spell to prove he could. Then when it went wrong, he cast the blame and responsibility elsewhere instead of accepting his failure and reattempting the spell he had just failed.
Hopefully that is part of his character arc in MM. I could see facing himself and having Mordo point out the concequences of his arrogance... perhaps nerf his powers a bit going forward by adding caution and more respect for the concequences of his actions.