I started at 14 years old and smaller than you, so we all start small bro. You can see from the pic in my avatar that being born small didnt mean I was meant to stay that way. Personally, I would say cut down the total # of reps, if I did 40 reps on any weight as a warmp up, it would probably cut my working weight in half. Myself, if I was doing your chest workout, I would do say 30lbs x 10, 50lbs x 8, 75lbs x 5, then your working sets. Thats enough to get the muscle warm, but not enough to fatigue it.