SlideIn too wide/don't work correctly with theme

I recently installed SlideIn. I am running a theme called City Desk by Gabefire, which has a featured image slider on the front page. When I installed SlideIn and activated it breaks the slider on the front page. That’s not the greatest thing in the world, but my main question is setting the width of the slider. I set it to 300px width, but it still shows up as a full width white bar. In order to not break the slider on the front page I made it so SlideIn only appears on post pages. Is there a reason why I cannot get it to default to the width I want?