The first length can feel difficult for reasons the stopwatch will never record.

A stopwatch records the swimming and nothing that came before it. It cannot count the changing room, the being seen, the small negotiation with yourself in the doorway, or the years since you last did this. All of that was real work and none of it appears in the number. People then compare numbers and conclude they are further behind than they are.

Count the unmeasured part as effort, because it was. Having done a hard first session, credit the getting there rather than only the performance. And when someone tells you they went at all, treat that as the achievement it usually is.