Hi there!
I am a specialised graphics designer focusing in the marketing/advertisement sector with multiple previous clients for whom I have created online stores selling a range of various products.
I have created multiple successful stores using shopify before so have plenty of experience with the website & how to use it (including using oberlo for importing products, usage of various themes, installing apps, designing custom images etc.)
With your situation i have an idea as to how to fix your image so that it will look HD in both mobile and desktop browsers!
I always stride to get your required task completed to perfection & on time and would love to chat via DM's/audio call/video call to make sure you get exactly the store specifics you are after!
Other than that, have a nice day & i look forward to potentially working with you!
Kind regards,
Alex :)