Your plan to ride the scary part this weekend is a good one. Practice is always good! I'm sure you'll quickly gain the distance...you can always commute on alternate days to start with.

My commute is not as intense as yours sounds, though traffic here is pretty *special*. You do become accustomed to the context in which you are riding, and your instincts and intuition are honed by experience. I think you will find that it does get easier, and riding the route on weekends to start getting used to it should help. The route of commute is also the route to a couple of longer rides, half way to the grocery, and the way to day care so I got to practice it a lot-- which helped me gain confidence and recognize road obstacles.

Over time, you'll become confident around vehicles, and learn to anticipate their moves. Somedays, you just won't be aces on the bike...or you'll be hungry, and not clip in properly or wobble to start, but because you've ridden and ridden that route, you know how to safely cross the intersection without even thinking about it.

Left turns become easier with time; some of the drivers let me take the lane when I signal and even yield when they should!! Others pass me on the left...or turn right and try to make me ride to their left. Look drivers in the eye whenever you can, it does seem to help. Crossing like a pedestrian is fine, but remember that bikes are hard to see anywhere.

The commute (for me anyway) becomes second nature, like breathing. As long as you're familiar with the route and stay alert, it'll soon seem natural to ride those scary places. Will scary things happen? Yes. But you will also learn from them and be a better rider, and probably not be hurt if you pay attention, use consistent behaviour when riding, wear a helmet and visible clothing, and use a headlight and blinkies at dusk.

I'm sure you can do it!