Not necessarily regret from being in the wrong industry, but:

I foolishly moved across the country for an entry level job as a contractor. Worked with this company for ~9 months, and I ended up quitting because my boss threw me under the bus for some really stupid design decisions he forced me to make (and I told him many times was not a good idea). He lied about it to upper management and I couldn't prove anything because all of our discussions were face to face (he outright refused to communicate via email), and so upper management denied my claim for unemployment. They also stiffed me for 40+ hours of PTO, which was a nice touch. They also refused to pay me my moving bonus, which I'm pretty sure is illegal but I can't afford to pursue it.

So here I am, jobless, no unemployment benefits, selling off personal belongings to pay rent/ trying to find another job with this stain on my career. It's not the optimum scenario, but I honestly prefer it vs working under a piece of shit manager.

The only reason I mention this is because you'll often hear people tell you to take the first job you're offered out of school because some experience is better than no experience, and that is demonstrably not true. Companies are out to take advantage of new graduates, and that can have a long-lasting impact on your career.