Dicky old boy, your minimum gross gradient in the second segment is 2.4%. So take a look at your V2 speed. Im guessing it's more than 120kts but lets use that as a convenient figure and go with still air so yer speed over the ground is approximately the same. Now in old money that would be 2 nm a minute or 12152 ft per minute. So your minimum rate of climb is 2.4% of 12152 =292fpm.
Hence 100fpm is about 33% of the minimum allowable climb rate!
Ergo you did the sums wrong.
Oh and an even quicker way is just times your groundspeed by the gradient to get RoC. I.e. 2.4 X 120 =288