Maybe post a few pics of your board?
Fins are a tricky one, some people love playing around with different combinations and sizes for different conditions but I personally hate it. After 25 years of surfing I have two sets of fins, one quad set and one thruster set

. There's just so many nuances with fins it's out of control.
Maybe you could track down a cheap old traditional shaped surfboard and give that a whirl and see what you think (something similar to the North wam if you're unsure.) Fins are so bloody expensive nowadays that it'll probably be the same price.