You should not owe an underpayment penalty if this is your first year filing a GA return (your last year GA tax liability was $0).
Check your GA forms. You should have submitted Schedule 3 to calculate the amount of income taxable by GA. You do not just file a standard form reporting only your GA income. You report all your income and a ratio is calculated, of how much GA taxes, is calculated (most other states do something similar). If you told TurboTax you were filing as a non resident, this should have happened automatically.
