Once you enter the finish funnel, timekeepers record your position and finish time then you’re given a finish token - the token crew are at the end of the funnel. You stay in order, take a token and then go and get scanned. Even if the person with your barcode finishes after you, your finishers token will record your finish time. I sometimes get my barcode scanned 10 minutes after I’ve finished as I’ve gone to meet the child or made my mileage up and my time is still my finish token time.
It’s also worth noting that your time is from when they say go and not when you cross the start.
I hope that makes sense!