If you want a gallery with attachment pages that do not allow comments, it can be done. You can't change the post you have now; you'll have to make a new post.
Before you add another post to your blog, go to Settings —> Discussion Settings —> Default Article Settings —> uncheck the box that says, "Allow people to post comments on new articles" —> Save.
Go to your dashboard and add a new post. Upload your pictures again. But be sure to give them new titles; if you don't then WordPress will do it for you by adding a "1" to the title and that makes things confusing. Add the "new" re-uploaded images and make a gallery of them. Now when you view the gallery the pictures open with no comment boxes below.
If you want comments on the post itself, then go back and edit the Discussion module on the edit post page to allow comments. People can comment on the post, but not on the attachment pages now.
Publish new post. Delete the original post/first set of images.