Why differentiate Catholics from Christians?

Hmmm... I have been trying to be a true CHRISTIAN (there's a reason behind that capitalization) for about 3 years now, trying to live that CHRISTIAN life and change my ways to comply to certain values I hold in accordance with the CATHOLIC CHURCH. Okay, now, why did I capitalize the two words? Cos, I don't understand how or why Catholics are NOT Christians. I go to a bible study at school and and I am the only Catholic Christian there, everyone else says thery are Christians and that I am a Catholic. What? When did we Catholics become NOT christians? I believe anyone who follows Christ is a Christian, I mean, isn't that the true meaning? That's why we call the religion Christianity and under that comes Catholicism and Protestant christianity(which some people do not agree with now a days). I would prefer differentiating denominations as 'Catholics and non-Catholics' to 'Catholics and Christians'. I am not against non-catholics because my friends in this group are some of the best people in faith so dedicated to learn and live that life which Jesus wanted us to live. I know it's not wrong to use such words but I just am unable to accept it when people say they are christians and we are catholics as if catholics are not christians. Well, just wanted to get this off my chest and there it goes.
I am also heart broken at that fact that some Catholics don't even know about catholicism which makes it easier for some aggressive anti-catholic men/women to attack cathlics whenever they get a chance. I remember one incident that happened a year ago when I went out on a summer BBQ at a local park with some of my bible study friends. We met some other friends of one of our friends from his church. We had good food and played football (not the american version of rugby but the real football which is the number one sport in the world ;-) ). And then there is this guys who comes to know that I am a catholic and asks me why we pray to the saint and Mother Mary. I was not prepared for such questions during that time and I just got away with vague answers like "it's not wrong to ask someone to pray for you". Then, the guy asked where in the Bible does it say that we should pray to saints, I could not answer that. I don't remember how that conversation ended but today I realize that it is the tradition which passes along generation by generation (from the first ever christians, the Catholics) due to which we pray to saints. St. Paul clearly says in his second letter to the Thessalonians that we should "...hold fast to the traditions that we were taught..." by them. But I do not regret that incident because because of that I came back home to search for answers and my interest in apologetics came to life. I am still a learner and I would never do this to offend the non-catholics but to defend ,clearly, for which the word apologetics stands. Now thinking about it, I remember this that I read in some website, "where in the bible does it say that we should look into the bible for reasons for catholic/non-catholic practices?". This would then, become a paradox by itself because we can't search into the bible to find answer to whether we should search the bible to find answers or not. Did that make any sense? I hope so. Anyways, I believe all the people are God's children and it doesn't matter what denomination we belong to, to be a Christian. Peace.