Is adding 1 tbsp of rice cereal per oz too much for six week old??

My 6 wk old could not hold down his formula so doc stated to add the 1 tbsp per oz. I know the doc said to do it but to me it seems like a lot. I have tried it and the spitting up/vomiting has stopped but I'm just concerned at the thickness of it at a early age. Also concerned about his bowels and if he will get colic and/or stomach discomfort.