Hi, Jennifer!
Great question!
The short answer? Nope! :-)
If you look at the online window for purchasing
Walt Disney World Theme Park Tickets, you'll see a little rectangle near the bottom of Section 2, labeled Important Multi-Day Ticket Details. This states "Tickets and any options purchased must be used within 14 days of first use." In other words, once you've activated your first use day (not necessarily the same day you purchase them), you have an additional 13 days to use the remaining days' worth of tickets.
Thus, relax and enjoy your trip to WDW at your own pace and on your own schedule, Jennifer. Tuck a rejuvenating resort day here and an afternoon at Downtown Disney there (no ticket needed), using those park tickets throughout your stay. It's a great way to stretch out the experience and relax at the same time.
Happy planning, Jennifer!
Be sure to send more questions as you think of them; we love to help!