You are being way too hard on yourself. You know how many times I’ve done the exact same thing? Many. Or when I do actually remember to ask for the time off, I’ll be sitting at my desk totally oblivious to the time and wind up being late. Don’t beat yourself up. At the end of the day, you did remember the appointment.
To help things out somewhat, I installed the Cozi Calendar app on my phone. It’s a family sharing app, so everyone in our family has the same calendar. And I can set multiple reminders. It’s been pretty helpful.