My blood test said negative for arthritis, could I still have it?

Yes. A significant number of patients with rheumatoid arthritis will have a negative rheumatoid factor at the time of initial evaluation. There is no single blood test which allows one to make a definitive diagnosis of ra. The diagnosis of RA is made on the basis of clinical, historical and laboratory criteria.
YES! Blood work is only one tool in the diagnosis and is not 100% accurate.