if you arrived on the 20th you actually need to put the 19th in Google to get the correct day count. The way you're doing it the 20th isn't counted when it should be
In theory you can get one 180 day extension at an immigration office inside Thailand but you need absolutely everything updated to the current point including 500k baht in a bank account for 30 days, and even then immigration make it difficult. Much easier to leave and return