On your BAS you need to be declaring ALL income in G1 and then ALL expenses in G11. The BAS is a very simple profit and loss statement to the ATO so they know how much you are earning. You cannot put your profit or loss as the Income in G1.
You must lodge your BAS if you have joined the GST system and have a BAS, they will be charging you $220 for every late BAS report.
You do not have to lodge BAS returns if your income is less than $75k annually but this is not voluntary, if you are already receiving a BAS statement then you must cancel out of that part of the system by writing to the ATO.