advice on a used car i bought?

[Jolene]

what should i do,after buying it,and before we drove it off the lot,the check engine light came on,and the sales man said he will fix it,2 weeks later "third time" having 2 bring it back because it wasn't fixed like he said he. What do I do,I payed cash for it and I even purchased a 90 day warranty. This whole thing SHADY and I love this car it is so cute. HELp