If you know that you have build only 27 links then why are you asking about Majestic? They are probably showing 873 no-follow links.

There could be a ton of different reasons why.

The most logical reason is you or someone was using blog comment spam as a method of creating links. Most sites that allow comments, have a "recent comments" widget on their site. Those widgets usually show up on almost every page of the site. If you made a comment with a link back to your site and it showed up in that widget at the time when Majestic happened to crawl that site, they are going to see a link on almost every page. Over time, your comment will roll out of that widget and not show up on every page anymore.

This can also happen on directories sometimes. Some of them have a "recent listings" type of widget that will cause the same thing.

Take a closer look at where all the extra links are coming from. If there are a lot of links from one or a few sites, chances are it is from something like this.