My first loaf! Tell me anything I've done wrong

397 g warm, filtered water 100 g active starter 500 g organic bread flour 12 g fine sea salt

Mixed and let rest 30 minutes, did 4 sets of stretch on 30 minutes intervals, then let rest until doubled (9 hours). Wrapped in plastic and put in the fridge for 20 hours. Preheated pot in oven at 500 degrees F, while I scored the loaf. Put into the preheated Dutch oven and covered, lowered temp to 450 and baked 30 minutes. Removed lid and lowered temp to 400 and let make 10 more minutes. Let rest on the counter until morning.