Chances are you can get out of the contract if you go to the dealer on Monday AM and inform him in writing that you want out of the deal. Most states have a buyer remorse law that allows 3 business days to cancel a contract. The info on this should have been in the paperwork you signed......you did read the paperwork, right?
Here's the bad news. The $1,000 deposit is generally not refundable. Most dealers will give it back as a good will service, but they don't have to. It should have been made clear to you at the time you made out the check that the deposit was to "hold" the car, and if you didn't take delivery of the car within a specified period of time, you forfeit the deposit. This is pretty much standard practice. I wouldn't put a stop payment on the check, as the dealer may be able to come back at you for fraud if you do, and then don't take the car.
If your state has no buyer remorse statute, you are pretty much S.O.L. After all, you did sign the papers, and probably one of the papers you signed was to verify that you understood the contract.
Here's some free advice: Don't ever sign anything you don't read, understand fully, and agree with. Ever!
Don't ever negotiate a car purchase based on monthly payments. Negotiate on purchase price, and figure the monthly payments after a price has been agreed to. If the salesperson continues to talk only in terms of monthly payments, get up and walk out. They'll call you back, and if they don't, there are plenty of other dealers.
Always try to have an alternative source of financing such as a bank or credit union. It sounds to me like you can't really afford this car, and if you had consulted with a loan officer at a lending institution, you would have been so informed, and saved youself a lot of grief.
My advice is to either negate the contract by legal means, if available in your state, (you should be looking that up on the internet right now), or simply refuse delivery of the car and eat the deposit. Remembering the $1,000 loss will make you more careful in the future.
Life is tough, my friend, and proceeding through it wit blinders on makes it even tougher.