Yeah, I think you are not assertive enough, and I am exactly that way. My husband tells me all time that I don't speak up until I blow up. For example, he takes his dirty dinner plate and puts it on the counter right on top of the dishwasher. Why can't he just put it in the diswasher? Makes sense, doesn't it? Well, this got on my nerves everyday and he had no clue. Then during a fight, I mentioned it and he told me, all I needed to do was ask him to put it in the dishwasher. So, now he does it. He had no clue it made me upset. He says I should have spoken up if something bothered me. He is a big beleiver in communication.
My sister and I fought like you today, too. Don't feel bad about yourself. I always keep stuff inside and be quiet to save peace. I don't think you will be judged to speak your mind. You will appear more confident.