Knowing what to say and who to say it to, as well as at the appropriate time, is a difficult art. That is something only you can determine through deep self-reflection.
I will state that if you are worrying your parents, you must examine your behavior and make serious modifications. Are you certain you are acting right by avoiding the ones you love? Are you truly helping them by hiding? Truly, this teaching should deepen self-understanding and comprehension of others. It should deepen our relationships and help us act in more positive ways towards the members of our family. This is part of the Aquarian influence.
However, this does not necessarily mean that you go and preach to them, since that could prove destructive. I remember helping one of my students who to this day still lives with family. When he first entered Gnosis, he became anti-social, reclusive, and rigid in his mentality. He "dropped a bomb" on his family by trying to teach them Gnosis, but in a very strong, uncompromising, and fanatic way, which forever spurned his family against the teachings and deepened their anxiety to the point they felt he needed medical treatment.
He learned the hard way that the best thing was to have kept silent about certain aspects of the teaching, because they were not ready for it. However, to explain how he entered into practices like meditation and was studying religion was not harmful for his circumstance, because his parents were open enough to "New Age" concepts and a resurgence of spiritual philosophy in the west, such as through the popular spread of Buddhism, Yoga, meditation, etc.
He now continues to live with parents, and is making great progress. More importantly, he is relating well with his family, and even while they still think Gnosis is a cult, they do not think anything is seriously wrong with him to the point of necessitating hospitalization, because he exhibits sane behavior, which is always how it should be! If our spiritual practice makes us dissonant with others, especially our loved ones, we need to re-evaluate our behavior and our mentality, because the Intimate Christ within our hearts should help us better relate to humanity, not distance ourselves from it.
You have to gauge your family. Only you know them. Are they Christian? Relate to them through Christ. Are they Buddhist? Relate to them through Buddha. Are they Muslim? Relate to them through Allah and His Prophet (peace and blessings be upon him). While I mention this, you have to understand that you cannot get on a pulpit with your family, but to fulfill your role as a good son, student, and disciple. The requisite of all spiritual development is to fulfill our role in society. Right now for you it is high school and your family. Therefore, work to fulfill your role as an essential component of your spiritual practice, not by abandoning your family.
If you want to be honest about your spiritual practice, then explain it to them. But what you should say in particular, is up to you. Only your Innermost can show you how to best relate to others. No one can guide you but God.
To conclude, honesty is the best policy, but this does not mean you overflow a person's cup, meaning: do not give more than what the other person can understand and carry. If you make a mess on the floor for pouring too much knowledge, you will be the one to blame.
And most of all, be at peace! Go have fun with your family, talk to them, and SHOW them that you love them deeply, since they gave you life and they are now deeply concerned with your health and wellbeing. Demonstrate to them that you know how to be a good child and that you appreciate their love for you. When you approach your family out of love, they will likewise respond in a similar fashion, and will also be grateful to you. To quote the Dalai Lama, "My religion is kindness."
Joyful in hope, suffering in tribulation, be thou constant in thy prayer.
Benedictis, qui venit in nomine Domini. Osanna in excelsis.
"Blessed is he who comes in the name of the Lord. Hosanna in the highest!"