The reason I gave you the link I did, was so that you can see what is and is not possible using gallery images. There is no custom gallery and you cannot use plugins here on a WordPress.com blog.
A lot of things are not possible on a WordPress.com blog whereas, if you were to self-host using a WordPress.org install, it opens up a lot more possibilities.
To understand the differences between what you can and can't do on a WordPress.com blog as opposed to WordPress.org install, please read this:
If you want to have a look at what's possible with a self-hosted blog using WordPress.org software, here's a link to their support site and forums:
However, be aware that anything that relates to a blog on WordPress.com (which you currently have) won't receive a reply there - you can only ask about that here.