since pre business/undecided are under the college of L&S, it will probably not be as hard compared to engineering. its comparative to other majors in the college of L&S cause that college admits students blind of their major. eg. if u applied pre biz and a person with the exact profile as you applied undeclared/psychology, they would have just as much chance as you in getting in.
Like all engineering oriented majors, it is difficult. I never knew that many people who were in it, but I understood it was not as hard as say EECS, but it was stll challenging. My sage advice once again: Study early, study often. Do not procrastinate and fall behind.
I am not in engineering but I would think engineering is not a competitive major, it is just extremely difficult. Engineers help each other out like crazy and engineers that do well as usually work with other engineers all the time.
I swung a 3.8 one semester, but I was a freakin' hermit. Maybe if I had studied one more hour a day or skipped dinner once in awhile, I would have gotten a 4.0 -- however, I found a good work/life balance and got a 3.5-3.6 consistently. I'd much rather have the slightly lower GPA and a much more well-rounded life.
Of course, I'm probably not as smart as some of the students at Cal (well, former student here), so your results may differ.