Is it necessary to eat 4 times (according to meal plan) a day ?

This depends on your body type, and your hunger. Each one's body is different. 

If you do NOT feel a genuine sense of hunger 4 times in a day, it is absolutely alright to eat fewer meals.

However, if you feel keen hunger multiple times a day, then we suggest that you do not ignore your hunger. Instead, satiate that hunger with pure, easy-to-digest, Satvic foods. 

We must listen to the needs of our body, and cause no violence to it.