there shouldn't be any *worries* ---- because there's many-more than one-way and/or road(s), to get to (and from) MoBay (i.e., the airport)

in fact, there're some GREAT-alternatives::::>> such as scenic back-roads. And/or go-via SavLaMar

as i recall, the marathon route is a loop,
which turns-around at GreenIsland:::: once you've gotten beyond that point, it's all-good (i.e., *normal*)

in-Jamaica, a *lesson* i've *learned*:::>>> there's DEFINITE-ly more than one-way to skin a cat.

again:::>>> NO worries..!!
... don't fret
'..they..' WILL get you out (& into) Negril ---- trus me --- you will NOT miss your plane

no problem