I remember when I took law in college that contracts are an agreement between two or more people to do something.

This means you cant force you to enter into a contract because of something you have done.

Me and you agree that if you feed me dinner I will pay you $10. Thats a valid contract.

You cook me dinner and after the fact tell me that I owe you money for the dinner. Thats not a valid contract. I didnt agree to anything.

Also you have to have all the parties of a contract in FULL agreement on what the contract is or the contract is voidable.

I agree to sell you my car which you think runs. You give me $100 for my car and then as you try to drive off find out the car doesnt work.