While the question is off topic, yes you got one chance about the Time KCSE results are announced where you can choose any course, a second chance where they allow those who chose all courses they did not qualify for to try to choose again and in some universities you can choose course or even transfer universities though this results in lost semesters or academic years. 
<div><br></div><div>At the same time, I think the discretion whether you will make the first 2 revisions lies with JAB</div>