Hi Scott
You ordered a basic bargain potted Bridgesii specimen. This is what cactus look like when they have been cut and grow new tips. It's not an issue whatsoever. They do Not grow flat on top of the other section. They grow from the side off of aereoles, aereoles are what spines grow out of. Also, it will not fall off, it's been like that for well over a year. This is cactus 101, I'm sorry you're a beginner, but I make myself readily available via email, text and even my cell phone to assist and answer questions regarding cactus. I want all of my customers to be happy and learn how to grow these awesome cactus successfully. Did you email, text or call me? We even include a card that that reminds you to reach out with questions. I Can't help and answer questions and concerns if you don't reach out and ask. Your specimen is healthy and will grow big if you take care of it. If you have additional questions, ask, and I'll answer.
Have a great day, cheers!