Google form and google sheet integration

Hi there , any one can help me out while i am trying to solve a auto billing automation i have made 3 product in my form wih quantity and have maintained the product table and have done all the function working already. but the thing is while i a customer submitted the query or the product , the cell that goung down while it inserting the new row and the previous row is down froom the previous, for that reason the callation is not being made with the effective products. If anyone from the community can help me out from the problem please mention the best way  to take over fuctionality of the automation smoothly. Thank you