Why isn't my slider filling up the screens width?

Defaultly if you put down a html code, it can be just as wide as the container it is in. We have a force full width option, which is a javascript code calculating the area left and right to the slider, and it gives negative margin to the slider to make it as big, as it has to be to reach the sides, but that has its limitation too.

You need to create a new module position, as you can see in here (lower at the "Creating new module position" title), or modify the css code of your template, that every container of the slider would have 100% width.