I am a nurse working three shifts

I am a male nurse working three shifts. On August 11th, while I was on my days off, five of my scheduled days off were cut, and four of them were sleep-off days.
While I was breaking down both mentally and physically, my team leader told me to sign a document stating that I had agreed to the schedule changes.
I felt so humiliated at that moment that I told them I would resign after working until September.
Then, that same week, we went on a hospital workshop where I won MVP in a team competition.
After drinking some Yangju, I intentionally brought up the unfair situation during the drinking session.
During a meeting with my team leader today, they scolded me, asking why I badmouthed them at the workshop and why I acted in a way that would only be detrimental to myself.
Was I in the wrong for speaking up at the workshop?