I think if you want to play a game you should play it on a system not a computer parents/you spend lots of money for things on there like tf2 they are asking for more money by buying money for your user thats just sad.
That's called "Premium content", smart one. This helps pay the developer's electricity bills and keep their servers online.
TF2 is completely free, save the Premium content in which you
aren't required to buy in the least bit. Buying steam games is as valid and solid as buying a game that comes with a case, only you can back up games to other computers with the steam cloud system.
Regardless of whatever your parents must have uttered during their sudo-parental howling, downloading steam isn't going to print viruses into your hard drives, if that's the case.
Plus on the bonus side, seeing as how you handle much of anything, you'd think the fact that there is no game disk to scratch would win you over instantly.
But alas, ignorance is a bitch.
I suggest to hold onto the $50. Put it in a bank account or something. Judging by how dear you hold that amount of money, it's safe to say this is the largest amount of money you've accumulated in your life time. I can tell you from life experience that a penny saved is a penny earned; not a single goes to waste.