No worries. You can install and reinstall as you want. The big difference is if you have an OEM version or a retail version. If you install an OEM version to the same machine with same hardware setup, or if you have a retail version you can activate it as many times as you want to.
OEM version can be reinstalled and reactivated only on the machine where it was first activated. If you change the mobo or other important hardware, or if you want to activate it on another machine you have to activate it by phone and explain why you need to reactivate it. Normally Microsoft trusts the customers and let's you do that.
So go ahead and reinstall.