This might sound really weird but I love backing trailers up. Doesn't help you much but I agree with Maura, you have to just get comfortable with it. The more you do it, the more confident you become and the better you get.
Now, the only way you will get comfortable is to keep doing it. It's kind of a backwards thing, turning the wheels opposite of the direction you want the trailer and I think our minds tell us it's not working. TAKE YOUR TIME and be confident in yourself. It just takes practice and it will click. If you have to pull forward to straighten it out, do it. There's no shame in re-adjustment! That's the smart thing to do. Oh, and don't be afraid to ask someone to guide you on the blindside.
In public, don't worry if anyone is watching. Most of them are thinking they are just glad it is not them behind the wheel.