In my experience CBs don't simply "swell". More often, there's some foreign object stuck in the CB trunk like sand or gravel. Especially if you can swing it freely. However, your case may be different, so you should investigate.
The best way to work at CB problems, if you have the space, is to
careen your boat (lay it on its side). This gives you equal access to the inside and underside of your boat.
You'll want to remove the CB completely. By extracting the pin and handle, you'll also see whether the square part of the pin is rounded, and by extracting the board, you'll be able to see whether the hole is rounded.
While you are at it, throw in a new gasket in (available from DR marine - phone works best).
It is possible for the CB pin to be too tight against the gasket to move, but it's also possible for it to be too lose and thus not engaging the square hole (in addition to leaking).
The sweet spot on these boats is to have the CB have enough friction to keep it down, but not enough to prevent operating it.
If you see some (partial) rounding, you can shim any gaps between hole and pin. I used a flattened bronze washer to stick to like metals. Has worked pretty well for me.
However, there's one element you have not reported on, and
it may be the real issue.: There's a gravity activated catch that locks the CB handle in the upright position. If it engages and you don't release it, there's no way to move the handle.
It's a little triangular piece. If you've taking apart things, make sure you put everything together the same way.