Focus is a big no, majority of questions are not examination based. I study off fitz and camb, fitz mainly for exam practice + past papers, and camb for explaining concepts and keeping up to date in maths.
Get a tutor to go through the syllabus with you, answering every dot points. In terms of textbook, I would recommend 'Physics in Focus' by Robert Farr, and Excel Physics for exam study.
Apparently only malnutrition affects your growth, other than that its just genes. Also if you are a guy you will most likely be as tall as your father.