Couldn't Undo a Zhonya in the shop

I bought Zhonya's Hourglass today, but I unfortunately did not remember if I had my Heartseeker's fully stacked, so I wanted to undo it and look, but I couldn't and that could affect stats I was playing with, which is important. I did not move an inch between those actions, so I did not left the base. I played Azir, if that helps with solving the problem.