I'm a beginner Web developer and want to show people what I can do? but is it bad that I'm using a template for my site?

If it looks good and works great and your clients are happy, then use whatever you like.

If it's a template that you didn't create or are unable to modify to suit the client's needs then you would need to think twice.

if you run a blog where you document your adventures of your steep learning curve it doesn't matter, but it certainly doesn't hurt :-)

how about a blog series of setting up your own website with content hosted on github with markdown and a static website made with jekyll or something newer like wintersmith.io

You're not supposed to be a designer, so it's fine ;)

As long as you know js, ajax, jquery & how to normalize a database, any design it's fine coz the functionality it's all yours.