That book is not a general intro biology text. If you want general bio knowledge, I recommend Cell Biology by the Numbers (online, physical book). That won't cover everything you might encounter in bio 101, but most of the stuff it won't touch on is pretty useless IMO (e.g. approximately nobody needs to actually study Punnett Squares), and it will probably touch on most of the stuff you'd see in an intro class.
To emphasize, classroom cell bio curriculums sometimes haven’t been updated in 20 years. I haven’t used CBbtN as a general intro, just as an occasional reference, but it’s quite useful. It approaches at an angle regular textbooks don’t cover, in a way I find of more practical utility as an biomedical engineer than most individual info bits I find in a textbook.
You may want to spend time with a regular cell bio textbook - learning the basic structure of the cell is key. Perusing CBbtN, you will probably have enormous gaps in your knowledge if you rely on it exclusively - not least because AFAICT it doesn’t have much in the way of self-testing opportunities. But a great resource, one to come back to and complement your other reading.
In general, there are no shortcuts in bio.
If I self study biology by reading Systems Biology will I miss anything important? In this context the failure I'm worried about is "ended up learning a specialized field of biology, and would have to spend extra time learning biology in order to pass standardized tests if I go to collage"