I feel your pain. My dad really pushed advanced math and science on me (more work, less play) throughout high school. I hated it at the time. But now I know I would never have had so many choices and opportunities come my way or been nearly as successful in life had he not done that. This is really a good attitude you have! :) I hope you mean it and can hold on to it because it is important and will pay off (for you) in the long run. And not just for you, but for your kids one day too.
However, as a parent (and grandparent, and now great-grand parent) and someone with lots of parenting experience, what I see is a kid trying to sneak around behind my back. Not cool.
If they discover your plans, that will really damage your reputation and any trust they currently have in you. Not good.
I recommend you sit down and have a mature conversation with them. Then see if you can negotiate some more time - with the understanding that any slip in your grades will result in less game time for you. This is clearly one of those situations where honesty is the best policy.
