With me, not showing emotion was a way of hiding my depression episodes. It was mania that was harder to hide, but still, I'd try my best to stay away from my family so they wouldn't notice. So, I'd say you don't have to "act" bipolar to have the illness.
You should go see a mental health professional if you want an actual diagnosis. Internet tests and quizzes can only get you so far.
I will say that you don't have to really act in the stereotypical fashion to have bipolar. There are things such as high levels of self control that can help prevent at least the most destructive behaviors associated with it. In my case, I think my anxiety about getting in trouble for anything and some irrational fears about spending too much money kept me away from doing some rash things I was tempted to do. It similarly kept me doing my schoolwork during depressive episodes. I'm also generally good at telling myself "you're really going to regret that later" when I'm tempted to do something destructive, and I can usually keep a lid on things that way. Especially since I have BP II and do not end up fully manic, I don't act like people think a bipolar person would act.
I recommend reading around on psycheducation.org. It has a lot of interesting info about the bipolar spectrum and screening methods that include things like family history and previous response to medications. You'll still need to see a professional for a diagnosis, but it might help clear up some of your confusion.
I don't think I "act" bipolar either. I have had issues with impulse control during manic phases but other than that I have kept the symptoms hidden. Of course then there's the whole idea of how should a person with bipolar disorder act. I'm a prison nurse and deal with people that have bipolar disorder every day. Some of them really have behavioral issues, others don't.
I would suggest getting an accurate diagnosis from a professional. If you are diagnosed as having bipolar disorder, I would suggest going to a support group. A support group will expose you to different presentations of bipolar disorder as well as putting you in a setting where you can relate and people can support you because they know what you're going through.