Well, that depends upon the cause of the problem(s). You may need more images, if there aren't enough to fill the space, something like what you are mentioning can happen.
But, and this generally happens in IE only, something like that can also happen if you try to center the gallery using align="center", the <center> tag or the text-align: center; style. There are ways to center it though without problem in IE, other browsers are fine with almost any centering method.
If you want more help:
Please post a link to the page on your site that contains the problematic code so we can check it out.