What size is my iPhone 4? I always thought my iPhone 4 was only 8GB in size, does this mean it is 16GB?
Yes, you do have a 16 GB iPhone. The other 2.2 GB are taken up by iOS, etc. See here for more information.

Your model, MC676LL, confirms this: it indicates that you have a Black 16 GB iPhone on Verizon. See this Bestbuy page for more info. The 8 GB phones have different model numbers.