Definitely get lessons, either TI or another type. I had several lessons before my first tri. Even though I could "swim" when I was younger, I assumed that I could still swim and I couldn't.

As an instructor observed me, she asked if I felt I was rotating enough. I said yes. She said "that's odd, because you're not."

It's difficult to know what you're doing on your own because it's not like you can see yourself. I even got a coach to do some open water swims with me and that made a HUGE difference. I didn't become much of a better swimmer but he taught me rest methods and ways to relax myself in the water. Open water doesn't creep me out that much but when I saw the weeds waving around at the bottom, I started thinking about seeing body parts down there. I'm strange that way. The coach told me to appreciate the beauty when you're out in the middle of the water and notice how peaceful it is. I can still hear his voice when I swim

You've got time and I think it would help you tons. I waited until about 4 weeks before my tri and I muddled through though I should've started earlier.

I think you will have a fantastic time on your tri and you WILL become addicted