Creating a page according to my own page template

Hi,
I’m now scratching my head for my gallery page. I use the lazy gallery as my photo page, and since the link for it is https://…../blog/lazy-index.php, I have to create a “Custom Link” for it as this gallery index won’t appear on my “Pages” category [the category that will automatically have my links if I create “Pages”.

Now I want to have my lazy gallery to be listed in the “PAGES” Link section, but how?

Last time, I asked how to make an archive page to be listed there, and was taught to write an Empty page, then at the optiosns area, select “Archives” in Page template. [there are only 3 options, Default template/Archives/Links]

So how to add my own custom template to this option or will there be any other methods to have my gallery page listed in the “PAGE” Link category in the sidebar? Thanks in advance.