I'm going to offer something else that you might want to think about.
In magic it is absolutely vital that our words mean exactly what they say. If magic is going to work it does so because it is driven by our focus and intent and ultimately by the words we use to direct the energy towards our goal. If one gets into the habit of lying, even if the lies are meant to do good and not harm, it means that over time our words no longer mean what we say. That can have a very negative impact on our magical workings. So it pays to not get into the habit of even "white lies" if you are going to go down a magical path of any sort.
I do understand how difficult it can be to have to deal with others who would frown on our beliefs. There will be times when it is wisest to simply not let the topic of our beliefs come up at all. After all, what we believe is a very personal thing and really not something that should be discussed with everyone and anyone we meet. That is one of the reasons that bases of the Witch's Pyramid says "To keep silent." So instead of telling your parents you are Christian perhaps a better solution would be to not do anything around them that would suggest that you are not. If the question never comes up then you don't have to lie at all.
I also agree with Hadit93 that while you are living under their roof you owe them the courtesy of not practicing your religion within their home. No one can control your thoughts, but in courtesy your practices should be done away from them. Think how you would feel in a like situation if it were your home. There is plenty of time to have an open practice of your beliefs when you move out of their home. Being Wiccan is a lifetime journey, not something that must be done right now. In the meantime, here are some things that you could be doing that are not specifically Wiccan, but which will help your practice down the road.
- Focus on academic studies.
- Read about different mythologies, cultures, religions and the history of ancient peoples.
- Learn about the natural world where they live (the animals, plants, trees, and geology of your part of the world).
- Attend spiritual worship services of diverse faiths.
- Write and journal their thoughts and feelings.
- Pray and meditate.
- Give back to the world through community service.
- Embrace physical, mental, and emotional health.