I am now 15 days late. I have take a urine test and blood test, both were negative for pregnancy. I am never late, and have never missed a period aside from pregnancy. Is it possible to get a false negative at 13 days late?

Not with a blood test, but you could have conceived very late in your cycle and even the blood test was too soon... and saying 'never' really doesn't mean much.
Every woman has something unusual happen with a cycle sooner or later, such as skipping one, or hitting early menopause.
We just can't tell you whether you are pregnant or not pregnant.