No need to worry. In another 8 days, you'll find that your son is not sobbing at all on reaching the school.
You'll then see or hear him say the nursery rhymes and so on in some corner..
You know what! I joined an evening P.G. course when my daughter was just about two. And so I used to leave her at the creche in the afternoon and my husband would pick her up in the evening.
I simply hated myself when she would start sobbing at the turn of the lane. And then after about 7-8 days, I noticed she had stopped crying. That's when I noticed that she had begun saying rhymes.
Soon, she began looking forward to going to creche.
It happened again, when I put my younger son in school. Though, I taught in the same school, my son cried almost all the time.
He finally adjusted. But yes one thing. This particular school and the teachers were not so affectionate as the creche my daughter went to. And so taking advantage of my husband's transfer, I took a break and had my son admitted to a good school with an affectionate staff.
Also, if you show remorse or guilt, your child will definitely not learn to adjust.
Best of luck & relax.