Just signed up for first tri

Just signed up for first tri, July 30th. Sprint 400y swim, 12 mi bike, 3 mile run.
I already run, not fast but can do 4-5 miles easily right now. Will be getting my mileage back up to 20's in next few weeks. Will probably do a few 5K's in preparation for the tri... and brick workouts too of coure. Last year I finished the Big Sur marathon (first marathon).
I did my first bike ride of 11 miles on Friday- it was a good first ride of the season. In the past several years I usually ride 20-25+ miles when I ride. I used to ride all over the place when I lived in San Diego and had no car. Completed the Tecate Ensenada over 20 years ago. My bike is an old heap circa 1981- but can't afford a new one I don't think the riding part will be too hard for me.
Swimming. Uh oh. This will be interesting. Not much of a background in this. I did swim a little last summer, I started from scratch and got up to one mile. But we're talking slow with lots of rest. This is what I will need to work on the most. If you watch my race, please don't laugh too hard.
Ultimately, I think I would like to do longer triathlons because I think I am better suited to longer distances but with my lack of swimming ability, for now I'm going to stick to the sprint.
I look forward to becoming enlightened on this forum!