Sorry, misread your code. Your code is kind of confusing. I don't really understand what you are doing....
To explain
Nrows=4
For I = 1 to nrows
By that your loop is set to 4, full stop
That will explain your I ended up being 4 and nrow at 8 (nrow=nrow+1)
When I gets passed 4, you exit your for-next loop