Is it okay to have a small amout of sugar in urine after big meal?

Not usually. A non fasting blood glucose of 125-130 is considered pre-diabetic, and though the numbers change periodically, those around 150 are considered worrisome and need investigation. You need a blood glucose around 180 to start getting urine glucose, so if you're having sugar in the urine, you should get this investigated.
It is never normal . To have any amount of sugar in the urine.