I'm in the exact same position, i'm atheist but have to pretend i'm a muslim
I just started university
it can be very frustrating when anyone talks about religion because you're just thinking in your head "none of this applies to me, I don't really care, I don't believe it" etc
but, for your own safety you have to keep shtum for now, just grin and bear it
As you get older, start thinking about finding a part time job and saving money, and do well and get a proper job for yourself too whatever route you're taking, if you're going to uni start really early thinking about careers etc.
Then once you've got a good amount saved up and you've got a new job after uni (I know it's a long time away), you've got to leave without telling anyone
and then maybe contact them some way or leave a note telling them you're an atheist and you've left
you really can't do it with them or sitting down because some muslim parents can be quite extreme when it comes to leaving the religion, they'll never treat you the same etc.
even if they're nice and love you, you can't take the risk