If you're having a problem booting one OS or the other, then you need to elaborate on what's wrong. Running the Boot Info Script
in Linux (even from an emergency disc) and posting the RESULTS.txt file it produces (as a link or within code tags) will help us track down what's wrong.
If, OTOH, you're booting both OSes and they're both working to your satisfaction, then it's fine. Linux can't "fake" Windows well enough to make you think you're running your regular installation when in fact you're running something else. All you're seeing when you start up is the GRUB2 menu, which is a boot manager
-- a program that gives you choices of what to boot, before any OS launches. A boot manager is a practical requirement on a computer that boots more than one OS. If you don't like the "look" of GRUB2, or if it's misbehaving in some way, then there are other options. It sounds like you're booting in EFI mode, so you may want to check out my EFI Boot Loaders for Linux
page, which runs down your options.