I have seen whales in Samana bay during this time frame. Mother and calf humpback whales.
Yes, it is very possible you might have seen a whale or 2 in Samana Bay in late March. The whales do not arrive together and do not leave together. Many whales are already on their way back.
Last to leave are mothers with newborn calves. As mountainannie indicated, a mother with a very young calf will be waiting until she believes the calf is strong enough to survive the trip to her feeding grounds, which might be Iceland.
But unless Kim Beddall knows that there are enough whales around to justify taking money for an excursion, she will have stopped the tours for this year.
However, not everyone with a boat of some sort is as honest with the public as she is. Which is why I advised the OP to check with the people in Whale Samana before giving anybody money to take them to see whales. If the few mothers with calves are not found, the money is not going to be refunded.
Thee is no better source of information on the whales than Kim. She is the founder of whale watching in Samana Bay.