The problem is I am not Catholic, but I am a Christian tho. She told me that she wont force me to become Catholic, but she doesn't know if we can get married if I don't Convert.
Catholics CAN marry non-catholics. I do believe you need to be a BAPTIZED christian in a major denomination. It would be best to talk to a parish priest and/or parish marriage preparation person to get the specifics. You should know that most parishes have at a preparation program for marriage.
Even if one spouse is NOT Catholic BOTH spouses have to agree and PROMISE to raise the children Catholic. My husband was not Catholic when we married (he converted about 10 years after we wed) so our wedding was a sacrament of matrimony ceremony without communion (Holy Eucharist).
Since you will be obligated to raise your children Catholic and therefore (implied) teach them this faith then you should inform yourself of the basics of the Catholic faith. I would also encourage your girlfriend to learn more about her faith.
One EXCELLENT resource is the Catechism of the Catholic Faith that can be purchased at any bookstore for less than $10. It is a good resource for the basic tenets of the faith.
You're a good and honest man to think of this very important issue in your future marriage. God Bless!