Given the cost of a hotel room, cabs and buses, and the inconvenience realistically spending 10 hours traveling (if you include waiting for the next available bus), changing your ticket really might be the easiest thing. POP can be a bit pricey, but check Santiago and Santo Domingo airports as well. Take a cab to the Caribe Tours depot in either town, they have buses leaving hourly for the North Coast, including Sosua.
Otherwise, it's Bavaro Express bus to Santo Domingo. Cab to Caribe Tours (or Metro Tours), then board the next bus to Sosua.
As you're arriving at 2:35, I'd strongly consider overnighting in Santo Domingo.