Namibia found the task of reaching Holland's target of 314 for four too much of a tall order and eventually lost the game by 64 runs.
"Obviously we are very disappointed, but we have to be honest and say we were nowhere near out best with the ball and in the field," said Kotze.
Namibia knew that if they were to grab an elusive World Cup win, then their best chance would be against Holland.
But centuries from Dutch duo Feiko Kloppenburg and Klaas van Noortwijk soon put a major dent in any lingering hope.
"Their two guys played out of their boots," added Kotze.
"We are disappointed we didn't go back home with a win, but I think we have learnt a hell of a lot
"Thanks very much to all who have supported us. Hopefully we've made everybody proud.
"Our aim is to try to qualify for the next tournament and to perform better than we did this year."