HelP! I have no admin accounts!!! I CANT EVEN SHUT DOWN OR RESTART!! WHAT DO I DO?!!??

PLEASSE HELP! I acciendtly made 2 admin accounts. I tried to delete one of them and i accidently unchecked the "allow user to administer this computer" for both of them. Now, I have no Admin account at all. I cant do anything without it! I can't even shut down. When I try to shut down or restart my computer, its needs my username and password for my admin acoount, and I DONT HAVE ONE ANYMORE! What do I do? Can I bring it to the apple store, will they help me? I just bought this computer less than a week ago. Can I return or exchange it? I HAVE NO WARRANTY!!!!! PLEASE tell me how I can fix my computer. Can I like restart my whole computer with no admin username and password? I want to fix it rather than get a new one. Do I have to buy something to fix it? Im broke, please help. IM WORRIED!!!! I cant do anything, I have no admin account!!!