How do I get out of a car finance without hurting my credit or the co-signers ? ?

You can't unless you crash it or set it on fire but then you'll be looking at Jail time.

Pay off the total balance in cash.

How do morons not consider affordability BEFORE signing a contract ? Sheesh.

You can not really. They will go after you and the cosigners and credit of all of you gets a negative hit.

About all you can do is sell it for what is owed on it since unless fully paid off it is not yours to sell. In a month and a half you probably can not get enough to pay it off.

You can try discussing options with your parents.

CarMax actually gives you 5 days to change your mind. That was your buyers regret window. Enjoy your Mustang.

You should sell it for as much as you can, then pay off the negative equity.

Tap your heels together & wish.

The ONLY way is to pay off the loan. Anything else will negatively affect your credit. Find another job so you can afford it.

Here's your two options:

1) Sell the vehicle for the amount of the payoff and pay off the loan in full. If you can't sell it for that amount, you'll need to come up with the difference in cash immediately so that the lender releases the lien and the buyer can proceed with registering the vehicle. 

2) Find a way to pay off the loan through your savings, borrowing from a family member, etc. 

There is no magic "right of rescission", no "buyer's remorse", nothing like that. Once you signed and drove off, it became yours.