I was just wondering if there's a way to disable to forward and backward navigational arrow thingys that Twine automatically puts on the left of the screen.
Yeah, absolutely! It depends what story format you're using. You can either disable the forward-back buttons or do what I do, which is disable the entire left sidebar. It makes for a more immersive experience.
#sidebar { display:none; }
You add that to the stylesheet to do that.
There are a bunch of good Twine stylesheets available on the Internet, too. If you Google, I'm sure you'll find some that you like and can modify to fit your game!