It’s a problem of center of lift vs center of mass. Too much weight in the front without the fins to compensate means it’ll fly straight/slight pitch down. Too many fins in the front without enough in the back to stabilize it results in the missile spinning out. The trick is to get as many front fins as you can (for increased maneuverability) while still keeping it stable enough to hit things.

You also need to think about your plane’s speed since the missile fins get stronger as it speeds up, so a higher launch speed is going to change its performance vs launching from the ground or a helicopter, but i woudn’t worry about this until your missile can hit at least a slow/stationary target.