ITC - Stock

dear team
Dear sir/madam,

I have a doubt regarding GST,

My doubt is that 

If I buy a product of Rs 100000 from my supplier on 31st of June and I received a ITC of Rs 4761.9 under VAT , on 1st July I sell the product with my margin of Rs 8000. What will be my tax payable under GST . If  GST tax payable is  18% how can I pay the excess tax still my margin is under 8%. is there any compensation?

Please help me to know 

My commodity is Tractors Sales