Need some advice, thanks.

Im 5'8 160lbs and I switched from my usual longboard 8'6, to a smaller board a 6'8 Retro Fish with a twin fin, made by zippi fish. I had one good day on it where i caught a fair amount of waves ( it was a sloppy day ) but the past three session have been pretty sad. I feel like i can't get into the waves correctly on this board. Im having trouble on peaky fast waves? I'm pretty sure this is not the boards fault? got any tips on how to handle this board. Should I have gotten a different board? Thanks for the help.