After I posted yesterday, I had to laugh at my ’fitness’ comment. I realize the only reason you float like a brick is because you’re super fit. Mussel and bones sink.
I believe the ’skill’ you’re looking for is - slow and long stokes with your arms. For your legs, I alter between a breaststroke kick.
With all water activities, being slow and efficient is the secret. I learned how valuable that is when trying to swim long distances underwater. Someone told me if I stop trying to do it as fast as possible I would go a lot further. That advise changed my distance from around 40 meters to double that, plus more than doubled my down time. Put yourself in slow motion and save your energy.
You can do this! 10 days to go.