Definitely give it a go. Don’t worry about running the full distance, if you have to stop after 4 and walk the last 1, there will be plenty of people in the same boat. On my first one I think I had to stop and walk parts of the route at least four times. But from there you’ll likely see a week on week improvement.
The beauty of the parkrun is how welcoming and varied the field of runners are. And being in an environment surrounded by others running and being cheered from the sidelines can really help to boost you to push that little more! Can’t recommend it enough.