regenerating thumbnails – wrong image sizes

HI
I resized my “gallery size” thumbnails to 845 x 400 and regenerated the thumbnails, which worked fine. When I did the same to the “featured_large size”, and regenerated the thumbnails, I also regenerated the gallery size ones again by mistake, but the size was still set to 845 x 400. Now on my portfolio items, those gallery images are displaying like this http://andesworldtravel.com/trips/col-32-lt/ instead of like this http://andesworldtravel.com/trips/col-26-lt/, even though when I go into the editor and re-add it the size is at 845×400 as it should be. Is there a way to fix this without going through every item and re-adding the image? It’s a big site. Thanks
Nancy

and yes, next time I will uncheck the boxes so the images don’t resize!