I actually don't do any situps for the most part. My core and abs get engaged when I do cleans and other stuff like tricep extensions. If I'm working more on core strength I more focused on stuff like scissor kicks and bicycle kicks in this laying down position.

You have to focus on having no space between your back and the ground. Like you did a little mini crunch the entire time you are doing this to really focus in the right places.

But in the end all of this stuff is good core exercises but really what is going to ultimately determine making your abs show is being lean enough. A lot of men store fat around their mid section so it will be one of the last places to burn off.