ANSWER:

This duaa is not from the sunnah as it is not authentic.

Simply say bismillah in the beginning and alhamdu lillah in the end.

Everytym b4 i eat i say allahuma bariklana fimarajaktana wakina adabala bismila & when im about to eat i say bismila den while chewing,in my mind i glorify da blessings by saying in my mind alhamdulila & mashaallah. i cant stop me saying that & i think only say alhamdulila when finish but really im not aware sometym. is it sinful to say that dhikr all the time esp.when not yet finish & say alhamd?