If there was really nothing wrong with the boy or girl (being rude,nasty to people or anything against halacha ect.)only not “hitting it off” together, I think they should give it another chance. They could be nervous and not really be themselves.
I know from experience, we just finished having sheva brachos for my daughter and her chasson. My daughter went out with her chasson on their first date which lasted only an hour, she came home and told me she had nothing to talk to him about and he was not for her, he went home and said the same thing. I pushed her to go out one more time and he agreed to go out again (the shaddchan had a lot to do with it) and the rest is history (it really took five dates before it really clicked). Now they have so much to talk about and are so much alike in their thinking and hopefully they will always stay this happy with each other.