Welcome to the site!
Believe me when I say that in swimming, you're already well ahead of plenty of people. This is a
very popular question on these forums, and I invite you to check out
the other threads discussing it for a
longer answer, or perhaps a
shorter one.
If you just need a quick reassurance: You're going to be fine. You're going to step off a short diving platform into the pool, swim to the edge, and then make it to the other end of the pool alive (50 meters I think, and they don't care about form). After that you'll do a prone float for 5 minutes, and then a coverall-inflate float, and you will not see the pool again unless you failed something.