Gallery pictures overlap boxes

I used the wordpress default gallery as per instructions, all images were set to 150 x 150 yet they still overlap the borders, this looks untidy and very sloppy. Gallery cannot be used

 

I found an absolutely phenomenal gallery plugin that I now highly recommend:

http://wordpress.org/plugins/easy-media-gallery

Take a look at their demo pages here:

http://ghozylab.com/new-feature-sample-1/

 

Next Gen Gallery is very easy and a good plug in to use also