I was curious if muscles are a clear factor for stage 4 because according to your well-developed calculator I'm a 3.3, which is plausible because I am a late bloomer. I started puberty around 14.5 and every factor suits me except muscle amount. I've always had muscles due to my parents, who are both well-above average in muscularity. Since I've been playing basketball for four years, I would be glad if there is still some room for my height to grow.
What most people view as muscular is having well-defined muscles. Having large muscles can make them easily seen, but so can having low body fat. For example, Giuliano Stroe is a noted five year old who is both lean and muscular. While he has amazing strength and definition, still his muscles are not large like an adult's.
What changes in stage 4 is that you can not only have strong muscles, but those muscles can increase in size.
In regards to your growth, what you show in the information you sent me is a steady growth of about 5 cm (2 inches) per year. Typically a growth spurt is defined as growing more than 2 inches in a year. Your current rate of 2.5 cm in 3 months means you are in your growth spurt now. How much more you will grow is not easily determined. Much depends on how long your growth spurt continues. Even after it slows back down, most boys grow another 2 to 8 cm during stage 4.
My guess is that since you are in your rapid growth phase, you have slimmed down, decreasing your already low body fat. This is making your muscles stand out. Thus, you appear more muscular than you did last year.
I have another obsessive mental problem, which is mainly caused by myself and the pressure connected with my sport and expectations. On one hand, I'm really excited and happy to know that my dreams might realize, but on the other I undergo these depressing and frustrating days, where I literally talk myself into believing the opposite: that O will never be tall and strong enough for basketball, etc. Do you have any advice for me?
First, I want you to read: The Ten Shortest Players in NBA History.
What I really suspect is going on is that during your growth spurt, the hormones in your body are going crazy. In turn, it causes your moods to go crazy. When emotions go crazy, put them aside as untrustworthy (Proverbs 28:26) and look at the facts. I assume you are on the school's basketball team, so how have you been doing? Are you going to college on a sports scholarship?
It is hard to play your best when your body is changing. You haven't come close to reaching your fullest potential. But your aim needs to be to do your best with what you have and not wish for something you don't have.