Of course 7 days in Marrakech is not too long but this depends on what type of traveller you are, explorer? If so then there are several places to visit outside of Marra, Essaouira as mentioned and only 2.5 hours away, Ourika Valley, the gorges, oh, and the Atlas Mountains.
Is there enough to do in Marrakech for a week?
6 nights / 7 days. With its labyrinthine streets, arching courtyards, tiered gardens, and complex mosaics, Marrakech is a city steeped in history and architecture, best navigated with the guidance of someone who truly knows the ins-and-outs, particularly if you only have a few days to spend.