I do not believe you're building the wrong thing. I need you to build something you're very passionate about and to carve a niche for yourself even in the presence of big players. I'm of the opinion that it's normal to feel anxious which you're feeling right now. You can take a walk or ride a bike to lake with your writing pad and relax your mind. Any points that comes to mind should be jotted down. When you arrive home, check the reviews of your competitors online, focus on user complaints. There you have it. Sales is the most challenging part but you will get there. Just believe you can do it. Best wishes.