The shoulder makes the arm I always say, so in order to get that nice round shape, you have to hit all three head of the shoulder. Shoot for 15 reps and pick a weight where you begin to struggle around 12 reps. If you need to rest a moment to finish them, that's ok.
We're all harder on ourselves than anyone else is when it comes to our body. We see every tiny imperfection, every dimple, line, crease, and fold, even though other's may tilt their head in confusion at what you're seeing exactly.
You want the body, the fitness, the health but you're just not sure you can.
How do you believe in yourself when you don't believe in yourself?
You have to DO what needs to be done, regardless of how you think you'll do.