The prediction of the final gravity has no bearing on whether the fermentation is complete. That's for when you are formulating your recipe, but after you brew, the yeast don't give a damn about your fg prediction.
As stated above, fruit beers take longer to ferment. I would not be concerned about four weeks. When visible signs of fermentation cease (such as airlock activity), take hydrometer readings every few days. When the gravity is stable for 3 or 5 days, then you are safe to bottle.