Your first 5K will be slow. It’s still a 5K.

Finishing and finishing fast are separate achievements, and only one of them is required the first time. A slow time is not a lesser version of the distance, it is the distance, covered by somebody who had never done it before. The clock is the least interesting thing about that day.

Go at whatever pace gets you to the end, walking included if that is what it takes. Write the time down without editorializing about it. Let the next one be a comparison with yourself rather than with anybody else out there.