You should be fine. When I got married 40 years ago, I just added my husband's surname to my maiden name on my passport, so I have two surnames on it [and nowhere else, all other ID is only his surname]. In 4 decades, never ever a problem, and my reservations only have husband's surname.
If you don't follow the Spanish tradition of using your second (maternal) surname it should not appear on your documents. I just leave that space blank, even though my mother's surname is actually a not-very-common but recognisably Spanish surname.
I think they are more focused on making sure the person standing in front of them matches the Picture on the Passport, more than the names matching 100% .. I'm sure many people have even MIS SPELLED their own names, or omitted parts of their Name . Typos do happen when ordering online , its not a perfect system.
i doubt they would Blink at such a variable , as long as Passport Pic matches the person standing there , Immigration in the DR will sort out the rest if someone is trying to pull a fast one .. I would not worry about it for a moment .
Especially if you check in online in advance and are holding the boarding pass as well.
Here is a novel idea, why not just call the Airline and have them correct the name on the ticket .. explain your concern and that you dont want any issues when checking in or checking you bags .. try resolve it at least 24 hours before departure .that way you dont have to worry about it.