I went from same position as you (survival swimmer) to a 2.00 min/100 Ironman swim in 9 months, so to oly you’ll be fine. Stuck with the lessons, and keep at your own practice. You’ll probably have some breakthroughs when you make big progress and other days you feel terrible. Drills and sets are fine but there was nothing like doing close to the full distance in one continuous swim a few weeks out from the event to give confidence. As Edukator says, buoyancy from wetsuit will help a lot. I sometimes use buoyancy shorts in the pool as a technique boost and to mimic wetsuit swimming, makes a big difference.