I'm planning to quit my job in a week or two after singing a contract with another company. At my current employer I have a full-time contract and at my next job I will get 6 month probation. The new job is in another city so I will need to relocate but before I can do that I must first buy a car. I was planing to get a small loan from the bank before I quit because I don't think I can get one on a 6 month contract. To do that I need my employer to sign a paper that says that he won't fire me in the near future. Today I brought my boss the paper to sign and I told that I need a loan for a car (in hindsight a mistake). The boss told me that she want to buy me a personal car as a gratitude for all the work I have done.
What do I do now? I can't quit now before I sign the contract with the next company. I can't tell my boss that I will quit soon because I don't know if she'll sign the necessary paper. How how do I reject her offer?