How to unlock the aspect ratio on a Whiteboard shape

I am using the Meeting Agenda Whiteboard Template.  I want to make the rectangle below the header (where we see Introduction, Topic 1, Topic 2, Topic 3, Topic 4) longer.  Resizing the rectangle only makes the rectangle bigger in all directions.  I want to type notes for the meeting agenda items under each topic.  If my text expands, does the rectangle automatically elongate?  

Thank you,

Iowa Farmer