I think Amazon fine print states that unless otherwise stated the device limit is assumed to be 6 devices. The OP did read his textbook on at least two non-Kindle devices (Chrome Cloud browser and an Android device), so his claim of only 1 device is BS. I bet if he owned four Kindles he could read it on all of them too.

But seriously, $450 for an eBook. @Blossom is right in that is too much for an eBook. He should talk to his professor, who probably wrote the book, and demand satisfaction. Or find another class. I realize this is a medical reference book, but it is probably best purchased as a PDF if the OP needs it in digital format.