How to fill a gap?

I have searched using key words and haven't found an answer - sorry if this has been posted before...

We have a newer home that we just purchased that has three full baths that have Aquaglass Gelcoat tubs and showers. When the builder built the house they never "finished" the gap where the drywall goes over the flange of the shower walls. I have one shower where the gap between the drywall and the shower is quite extreme - 1/2" approximately. How do I fill this in - I am assuming that I can't just use silicone caulking?

I would be more than happy to put up a picture but I don't have a place to host it...

Any help would be appreciated.

Eric

You can post a pic in a reply - scroll down when making a reply to manage attachments under additional options. Note, you will have to resize the resolution and size of the image to be accepted (maybe 50K? I'm not sure), but it will work.