Weird URL duplication problem

Since I’m new to Hugo, this is probably a really basic question, but:

For my personal website, I have this projects page that links from the homepage, ie.

username.github.io/projects/

When I run hugo server, the link loads fine - it leads me to localhost:1313/projects/.

But, after deploying my site on github pages, the project page also loads, but the URL shown is

username.github.io/username.github.io/projects/ seemingly duplicating the baseURL o.O

In my config.toml, I have the baseURL set to http://username.github.io, and I have a menu variable:

[[menu.main]]
    url = "/projects/"
    name = "Projects"
    weight = 1

For reference, I have several sections just like this, all getting the URL duplication problem. I’m also using my own theme, which I’m currently making, and it’s in the themes folder.

Please search the forums, GitHub URL issues have been answered many times over. Also, please read Requesting Help before posting a support question, and include your code. No one can troubleshoot your config without reading it.