Triple jump question to all you Track and Field masters?

ok. so, i am in seventh grade, and my triple jump coach told me that it is bad to jump To Far on the first fase (the first jump). How is this true? And...when i take the step inbetween the two jumps, i always pull a muscle at the back of my leg. how do i stop this? Thanks in advance.|||Im a 9th grade guy, i did triple jump in 8th grade track. I won my conference with 37 ft 6in. The best way i found to lengthen by jump was not by adding a foot and 6 in. to my first phase, or 3rd phase, but by adding 6 in. to all 3 phases. also by jumping from a board farther back, so it is a struggle to get into the pit, will make you go farther (hope i helped)