If you got a smaller plant to start with it takes two or more years to get a lot of berries.

Scott

Pruning the tip of the lone primocane is not likely to spur growth of more canes, but it will cause lateral branches to grow out of the main cane.

If those floricanes are short and spindly, the whole thing was probably dug not long ago, and as Scott said, it will take time for the clump to get going. That's a fairly large pot, but it may hinder production long-term. Put plenty of composted manure or other fertilizer on it in the off-season, November through March.