I went back and looked at my HELOC 1098's during the draw period back in 2017 and they show the balance of the money I took out as of January 1 not the credit limit amount. It seems that entering the credit limit amount as the beginning balance will skew the average balance against you when figuring the amount of interest that is deductible. Remember that the money drawn form the HELOC has to be used to purchase or significantly improve you home.
I can't advise you on what to do as far as entering you HELOC 1098 into Turbo Tax, just letting you know what my HELOC situation was.
