It is possible to have chosen the wrong cat for your situation. A kitten in general may not have been the right age for you. But her behavior is NOT due to being a shelter cat. Everything you describe is perfectly NORMAL. If you need to take her back, then please do so. No one will be angry. But I would suggest re-thinking getting a new cat. If you need to have a calm kitty, get an adult who has already shown that he/she is calm. Kittens have energy and she is using it the only ways that she can.