Ancestry--I don't know any non-Orthodox Jews who would say you're not Jewish, even if you're mother wasn't. You're one-quarter Jewish ethnically, but you're a Jew, and Judaism is your religion, even if it's the religion you don't believe in! For that matter, your mother is also Jewish. To be honest with future suitors, you should tell them, "I have a diverse ethnic background, but I was raised Jewish and consider myself Jewish, but I'm not observant." There, no thank yous required.