It doesn't make you racist since you didn't know that you couldn't say it or if it would offend people.
However, since you're not jewish, it might have offended some people in the group but it doesn't make you racist for that single act.
Let's say you have a little brother. You pick on him and beat him up, but if someone else messes with him you'll kick their butt.
What people think is correct:
"It's okay for Jewish people to talk about themselves.
It's okay for African Americans to talk about themselves.
It's okay for Germans, Christians, Mexicans, Pacific Islanders, LGBT's, Obese, and Asians to talk about themselves, but it is not okay for anyone else to.
It's just rude and disrespectful."
My opinion (and it is just that), if you can talk about yourself and get upset when someone else does, YOU have insecurities. Now your joke was overboard (more like a death joke), but it DOES NOT make you racist. If you meant it as a harmless joke and it hurt someone's feelings, then it was a mistake because it was intended to be that way.