Hey there Torrey,
Welcome to planDisney and thanks so much for your question! You have a year of fun ahead of you with your Magic Key!
According to the
Magic Key terms & conditions, "The number of theme park reservations that may be held at a time during a Disney-designated reservation booking window is dependent on Magic Key pass type and is subject to availability of park reservations allocated to Magic Key passes and applicable pass blockout dates."
To put this another way, there are a number of details that could be behind you not being able to make that additional theme park reservation. It could be because you've reached the limit of number of theme park reservations that your pass can hold at any one time, or that the additional day that you're looking to book is on a blockout date for your Magic Key type. It's also possible that when you originally checked, the dates were not available yet on the
Magic Key Calendar.
If you haven't already, it would be worth checking those details above for your specific Magic Key, but if you're still having trouble figuring out what's going on then you can
reach out to a Cast Member at the Magic Key line who can better help you with the specifics of your situation.
When you're ready, then you can visit the
Park Reservations page to start the theme park reservation process.
Thanks again for your question, Torrey! I hope you have a fantastic time at the Happiest Place on Earth.
Have a Magical Day,
Greg