Swimteam was so long ago

I'm training for a sprint triathlon and today was the first day I hit the water towards that goal. The best I was able to pull out was 300 yards in 4 x 50 and then 4 x 25 sets. It's been 20 years since I was on swim team and my form was terrible, but mostly my arms are very weak. I've trained running and cycling well enough that I'm ready for the sprint triathlon in that department, but I've only got 2 months to get my act together in the water. I know I can do it and am following the Zero to 1500 plan (or will be, I was actually able to do W1D1), but I felt weak today.