Thats fine, you didnt contaminate it.
I usually scale it first then using a pair of scissors or a good filet knife i cut off all the fins, including the tail. Then I make a slit from the anus to the gil...all along the bottom of the fish and then I scoop out the insides with my finger. I then cut the head off right behind the gills and rinse the fish off. Thats it your done.
When you catch the fish its better if you reach into its gill and pull the gills off then hold the fish by the tail. This drains the blood and keeps the meat of the fish a lot better, it`ll come out pure white when you are done dressing it.