GSTR 3B RETURN

Dear sir,

I have not submitted my feb 19's 3b return and there is liability to pay tax....If today I am submitting my return , definitely I will have to pay late fee for that but my concern is about Inerest.

Do I need to pay interest also....gst site itself calculates the late fee but what about interest....???

So please let me know the interest provision in such a situation under gst...