Need help! to save paying gst.

Hello,

I am doing ecommerce business, selling clothes through my own website. Hence i took GST Registration voluntarily because i am selling inter state. Turnover not exceeding 20 lacs since im a startup.

So now, along with this ecommerce business, i also wanted to provide digital marketing services within my city.

So do i need to charge 18% gst on this service? 

As per my knowledge and research, i think i will have to charge GST on bills raised in this digital marketing service. 

Is there any way to avoid it? It will unnecessarily increase cost of service.