Put it in your calendar and show up. Reliability is a skill, not a personality type.

Reliability gets talked about as a personality you either have or do not, which is convenient for anybody looking for a way out of it. Mostly it is a system. People who always turn up are not more virtuous than you, they write things down, they leave earlier than they need to, and they decline things they already know will clash.

Stop trusting your memory with other people’s plans. When you say yes, put it in the calendar right then, travel time included. Do that for a month and you end up with a reputation you did not have to be born with.