I am pretty sure I am not cropping the thumbnails.
I did reset the size of the thumbnails and then chose the Create new thumbnails in the Gallery itself and they did resize to the larger size.
I tried inserting the Gallery again, rather than assuming that the initial gallery insert would update with and the images are still clipped off because the thumbnails are bigger than the box they are being put in.
I have seen the Clear cache folder but have never known what it did and so was reluctant to explore, just in case I did something that was not reversible. Can you explain what Clear the cache does?
thanks for your help.