I'm not an expert on this film (although many people have emailed me thinking I was an expert just cause I wrote the page on the film, hehe), however the poem was supposed to be written by Rocky Dennis. Whether or not it really was written by him, I'm not sure, but the movie claims that it was a poem written by Rocky for a class assignment.
Rocky reads the complete poem to his mother about halfway into the film when she is hurridly getting ready for a date, so you might want to check out that part of the movie so you can copy down the complete poem =-). Hope that helps