Just started CPAP therapy, diagnosed years ago.

If it were me and the only leak I was getting was like yours from last night....I wouldn't mess with a chin strap.

1....we assume mouth breathing leak but it could also simply be mask movement issue. To know for sure you have to tape the mouth shut and have the tape stay stuck all night.
2....if the leaks didn't wake you up they aren't really bad enough or prolonged enough to really make that much of an impact on your therapy.
Less than 1 % of your night you were in large leak territory....I don't even bother to bat an eyelash over leaks unless I have 20 % or more of the night in large leak territory as long as it doesn't wake me up.

Now don't get me wrong....any leak (no matter how big or how little) that causes us to wake up needs to be dealt with but because it is disturbing sleep and not so much because it may be negatively impacting therapy itself.