HELP, WHAT WOULD YOU DO?

You took the apartment/house at $2400 a month so obviously it's not a great hardship to pay it. The landlord can do all sorts of things legally to make your life miserable. It might just be best to notify them of the error and tell them you'll pay the rent you agreed to but you'd like a longer lease, free cable, or something (it never hurts to ask). Because, with the dog, they can probably boot you at any time because you broke the contract, so you want to be on their good side.