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.