how can i have a "x 4" pentagon then? AFAIK there are only 3 goals.
I can't say for sure. Someone mentioned here that you'll get the number of pentagons multiple of times you've reached a goal. I.e. if you did 200 words you'll get 2 pentagons for that. Personally, I'm more inclined to believe it's a glitch with over the midnight learning sessions, i.e. you've reached some goals before 3 a.m. and the next day. Pleas let us know which one of those versions is correct in your case.
Also, i have a "x 3" on a day with only 72% correct. (like the OP, in fact)
"80% correct " considered achieved the first time you've crossed the threshold. I.e. if at some point of the day you did more then 10 words and 80% of your answers were correct - you've reached the goal. The goal is not reset if correctness rate decreased during the rest of the session.