Definitely take a riding course. It sounds like you don't have even the beginning knowledge needed for riding in the city. The course will not only teach you how to ride with traffic but it'll make you feel much more secure doing it. At the very least use the internet to read up on it. There are many common sense rules that people don't think of until they read it then it's like a bulb lighting up.

It doesn't make sense to new riders but riding on the street is much safer than riding on the sidewalk - and much faster.

I was pretty scared of riding in traffic when I first started but I've become "comfortable" now. My commute is along a very busy street and it was downright terrifying at first but once you learn what you are doing and get confidence it's no problem. Take the lane when you need to to be safe and don't worry about holding people up. Of course be courteous when you can but it's better for them to have to get to their destination a little slower than to injure you. Being overly courteous can get you killed.

WEAR A HELMET.

It also sounds like your bike is either too big for you or isn't adjusted correctly. A bike shop can help you with fitment.