I have a few handguns to include .45, .357, .38 spl, .380, .32ACP, and .22 rim fire. I also have absolutely some of the finest holsters and belts.
Most of the time I carry a KT P3AT in a Fobus paddle holster. I don't care what the instructors say or the "experts" so called. I trust the .380 under most circumstances, and the light weight and size are so much easier to carry.
Few if any cartridges are capable of "one shot stop in the tracks" power. If you like the .380 get it. I doubt the instructor would want to attack you if you were carrying the .380.
Get what you are comfortable with and can shoot well, and pay no attention to the self styled experts. FWIW many CWP instructors are not especially knowledgeable in guns, carrying, or even the law. They just teach enough so that you can get a license, and they collect the money. Very few are truly gun experts. From your post I doubt your instructor is.
Rockinguns has it right.
Best,
Jerry