Mailchimp HTML Template - Responsiveness Fix

I have an existing Mailchimp-ready HTML template which is failing to render neatly on some screens. Need it proper on Gmail.com inbox/app, Apple mail, on Mac Book, mobiles and desktop. Budget - 15$ Timeline... (Budget: $10 - $30 AUD, Jobs: CSS, Email Campaign, Email Marketing, Frontend Development, HTML, Mailchimp, UI / User Interface)