Car dealer trying to reneg on contract

Hello I would like some legal advice.

I’m supposed to pick up my new car on Monday. I already signed the bill of sale, including the financing terms which shows the term, payment amount and how much interest I’m paying. I even initialled by the terms.

Now the dealer is trying to tell me I put too much of a down payment down and they can’t give me the finance rate. I either put $2.5k less or they can’t finance me this rate. I talked to the manufacturer and they are no help at all, I called the government authority and mentioned to them the situation. They explained to me that since the bill of sale is signed I would need to seek legal help.

If someone can give me some advice I’d really appreciate it.