Position elements in Gallery

I'm using upfront Gallery in builder and how you can see in this image
I see that they are floating left, but I don't know how make that they align in center.

Another question is:
The image that gallery use are cropped 200x200 and some of them look bad how you can see there " http://www.psworks.es/wp-content/uploads/2017/04/mango1.png "
So, how I can say to plugin that not crop the image? If the plugin doesn't crop them, it would look like this " http://www.psworks.es/wp-content/uploads/2017/04/mango2.png "