Chunkyd - Do you have a swimming pool or YMCA near you? Ask them if they have a swimming coach that you could hire to work on your stroke if you really are worried about it. Remember on the tri that you don't have to only swim in "Front Crawl" also known as free style. You can swim anything you want.

I went from over 360 down to 235 and went from hardly walking two miles to running 5k events. I also swim, lift weights, elliptical, bicycle, etc....... My RHR went from 75+ to 50 or less.

Just keep working on it slowly and it will improve. Just remember to gain no more than 10% of your distance per week and even that will be very difficult.

Keep up the good work and have a great time getting there and then completing your first tri!!!!