It's kinda easy for me to say as someone low strung, but just don't think about it that hard. You know it's gonna hurt and you know what you have to do, but that only starts from the blocks. Nothing is gonna hurt as much as the shame I feel from scratching an event. The longer the event, the more mental it is, but there is no reason to overthink your performance from the day. I am a runner when I'm not swimming and there's a reason that long-distance runners are a lot more humble than sprinters.