Creating a Shortcut to add calendar event

Hello. I am trying to create a shortcut that creates a calendar event so I can keep track of my assignments' due dates. I need it to perform the following actions: Prompt the user for which class, Prompt the user to name the assignment, prompt for date, and then add that calendar. This is what I have so far:

The contents of each of the Add Event block are the same as the first.

My issue is that this does not work on a Mac and only occasionally doesn't work on my iPhone--couldn't tell you why. On the Mac, sometimes it just fails, sometimes it results in the error "Attempted to save when persistence was unavailable". On my phone, sometimes it works, sometimes it results in the error "No calendar was set". The instruction set has been the same for awhile.

Can someone help me understand why this doesn't work all the time and a solution for this? Thanks!