Pre-reqs to a major are the most important classes. If your major requires, let’s say, 5 pre-reqs and you wait until the spring before you transfer to take them all, that doesn’t look good. It’s not really a situation anyone would find themselves in, but if a person were in a situation like that, they’d be admitted without the admissions people not really having a chance to see how well they would do in the classes most relevant to the major.
You want to go to Haas, right? Plenty of Haas applicants are taking their semester of calc in the spring before they transfer. I sit next to one in my calc class, and I’m one as well. It really isn’t that big of a deal and the only way it would be an issues is it you failed because there’d be no opportunity to retake it and you’d have to wait a year and apply again.