Can I make the Start/Finish line wider, so all of my laps will register?

You can make the Start/Finish line wider, but lap time accuracy will be poor for the laps that are not detected with normal 50-75 meter wide trap. RaceChrono will calculate the laps again when you edit the track, so you will get lap times even for your existing sessions.
Here’s the process:
1) Open your session, press the round “track” button
2) If your track is downloaded from, or submitted to the Track Library; you will need create a copy of it first: tap the copy button on top of the screen
3) Tap the Start/finish trap marker
4) Tap the edit button on bottom of the screen
5) Tap the width icon on top right of the screen
6) Scale the width of trap to make it wide enough to cover trajectories from all laps
7) Go back to your session, and the laps are now recalculated