That is something of a picky question, but the correct answer is better than the one you gave. The main reason for this is that the whole point of the colonies was to bring more money to England.
Your answer is not far off, but it is not so clearly connected to the idea of bringing money to England. England might like more population in the Americas, but that was not the real goal. The real goal was more money. England was not really looking for new trade routes with the colonies in the 1700s. Instead, it wanted more trade on the routes that already existed.
So really, I think this is an issue of emphasis. The correct answer clearly is talking about money. It emphasizes profit. By contrast, the answer you picked does not emphasize profit and does speak about population, which is somewhat irrelevant.
Again, I would say that this is a pretty picky distinction, but the point your teacher is probably trying to make is that the British were happy as long as the colonies were producing a profit. They wanted the colonies to make money that would end up in Britain.