Hi Erika,
This is a common question, but unfortunately the answer is no. You can get the latest information and prices on Magic Your Way tickets
here. With a base Magic Your Way ticket, you can only visit one theme park each day. So for example, if you have a 5 Day ticket but you are only going to be in Walt Disney World for 3 days, you can not use your "extra days" (ie days 4 and 5 of your ticket) to visit a second theme park on the same day. You are, however, allowed to exit and re-enter the same theme park on the same day. So you could visit the Magic Kingdom, go back to your resort hotel for a nap, and then return to the Magic Kingdom that same evening.
If you want to visit more than one theme park on the same day, then you have to purchase the Park Hopper option. You do not have to purchase this up front. You can wait until you get to Walt Disney World. If you actually go a second theme park on the same day, then you can just purchase the option then. Just remember that the cost for the Park Hopper option is the same regardless of whether you purchase it on the first day of your visit or on the last day.
Have a magical vacation!