Can I still negotiate the price of this car?

So on friday I went to a dealership and put a $100 down payment on a 2002 Honda Civic to get what was looked like an anti-freeze leak fixed and everything else wrong with the car fixed like new brakes.

I negotiated a little but not enough, I knew the cost of the car was $2100 because I checked Edmunds and told it to the guy and he said $3100 was as low as he goes when before that he said $3700 was his lowest, so I knew I definitely could of negotiated more but sine it was my first time and I didn't have much experience I thought he was serious when I gave him the price of what it's worth on edmunds.

So basically, after I gave him the edmunds price and he told me 3100 was is lowest I was happy that I,d save a couple hundred so I agreed but now I am definitely going to need money for other things like insurance and a new laptop my brother just broke that was $200

So basically, I only gave him $100 down payment and when I see the car again I am going to test drive it to make sure it's all good