I got it although used by some speakers to mean "i have understood" is not good English, you could be saying something like you have got a highly infectious disease and that every body should stay away from you, because they will die, and so will you within the next week. When you say "I got it?" got what? what exactly are you saying?. You have selected a not very good correct answer. You have not understood you did not "get it" if you did not "get it understand", you can't say "i have got it" because you didn't "get it".