Just keep telling yourself: "No one can make you feel inadequate without your permission." Make it your mantra, primarily because it's true. The one who was inadequate was the instructor, and I know because I've been an instructor many, many times.
In order to give a good class, you have to have a well organized plan. That means that if people need supplies, the instructor needs to inform them of this via a supply list. She should also have back up supplies, and not just dull rotary blades, and the like. That's demeaning, and it's meant to be. "Come late or unprepared, and you get the dregs of what may be left." That's just petty.
The class needs to be well organized. You would not have come away feeling disorganized if the class had been well organized, and that falls entirely on the instructor. The instructor needs to be flexible, so someone arriving a little late does not disrupt the flow of the class. I always had people arriving late, and I'd pair them up with someone, or a couple of people, who had been on time, so they could catch them up.
The truth is, you had an instructor who may have had excellent knowledge and skills, but no clue as to how to get them across properly to her students. She was inadequate. And because it's hard for you to believe that she could be inadequate, you are taking the inadequacy upon yourself. Stop it already! I'm sure you are a wonderful quilter. And please don't let this stop you from going to future classes. But do yourself a favor next time. Go prepared, just in case.
Warmest Regards,