Hi Braceton,
Welcome to planDisney!
Your planning is fantastic. Let's see if we can figure out what is happening with the tickets. My first thought is to doublecheck the type of 
vacation package you are booking. If you are trying to book a 
Special Offer, the offer might require a minimum number of days for the theme park tickets. When making the reservation, check to see if the system has selected a special offer and then check the details of that special offer. 
Try selecting just a Package and then see if you can select two day theme park tickets. If that does not work, you can try booking the 
resort hotel and 
theme parks tickets separately. Of course, I understand if you want a vacation package because you may want to add one of the 
Disney Dining Plans to that package. There could be other technical issues with the system as you try to make that reservation, so feel free to 
call to speak to a cast member in Disney Resort Hotel Reservations if you still have trouble making a reservation.
Braceton, once you have that reservation confirmed, consider the other special experiences you may want to enjoy. One of our girls loves learning about the animals at Disney's Animal Kingdom, so we have done 
Caring for Giants and 
Up Close with Rhinos. Keep exploring all that the Walt Disney World® Resort has to offer and let the planning continue!
Magic and memories,
Donyell