I am not sure exactly how VM works, but mine is always huge too. All I have done since I booted my computer 20 minutes ago is surf the net, and my VM is over 100GB as well. So there really isn't a need to worry about it.
It's no problem. That's comparable to your bank giving you a million dollar overdraft; you don't have to pay interest on that, only on money that you actually borrow.
What is there to fix. The OS is working as expected. One great thing about OSX is its memory management. If you start trying to "fix" it, then you may start running into issues.
Let OSX do what its designed to do and not worry about it.