I bought a used nissan altma with 100k for 5500 bucks two days ago in massacusetts and check engne light came?

i bought a used nissan altma 2002 with 100,000 miles fo 5500 bucks.... iput a dwnpayment on car fr 3 grand and signed no paperwork until ten days later when i brought te oher 2500 hundred to them...now the car wasnt registeredso te dealer put his dealer plate on car nd drove it with me to my house... while he parked it i noticed a big dent in front bumper so i touched it and pain was wet... i instantly told him i didn want the car one hour after puchase... tey told me they were closing in five minutes and to call them monday mornand theyd refund it... monday comes and theysay we wont give you a refund they say we will give you 500 dollars back for car but we are takin away your 30 day warranty and your getting car as is !!!! i replied no i dont want the car refund te money and they refsed and tld me to take it to court... i haea newborn andno vehicle so i took the car and signed a paper saying im taking the car as is cause i had no choice i dont hav months to wait to fet my 5500 back for a new car .... i registered the vehicle and insured the car and got a sticker now the day after i got the sticker the chck engine light came on and the cars makin funny noises!!!! what can i do ive owned the car for 3 days and they ar srewing me!! i live in massacusetts and was told you cant get a ca from a dealership as is under used car warranty law in massachusetts if it over 700 dollars and under 125000miles you get 30 days under the implied warrant of merchantibilty... what options do i have in mass legally i was also tol any car in mass under 125k and ovr 700dollars has to com with a warranty and they didntgive me one what can i do i now have a car with dented hood and check engine light on all becase of them the hoods messed up and now the check engine light is on and its making noise ??? what can i do to get this fixed by mass law or can i get a refund its been 3 or 4 days since i bought it ????