I believe the Catholics in Maryland were greatly outnumbered by the Protestants at the time of the Revolution (in fact, Protestants had always been a majority there). Maryland had 320,000 people in 1790, about 8% of the total US population of 3.9 million. The Catholic population was something like 1% in the US overall, and not all of them lived in Maryland—even if they had, they’d have been only 1 in 8 of the population there.
Catholics in Maryland nonetheless represented the elite in the state. Roger Teaney, the first Catholic Chief Justice, was a part of the Maryland Catholic elite. As a matter of fact, Catholics were one of the wealthiest religious groups in the country until the masses of shanty Irish came upon our shores, sending all socioeconomic indicators down for RCer due to their sheer numbers and poverty.
They were, but Catholics were greatly influential in the colony and were represented at the signing of the Declaration.