Guidance for my Android app that got soft rejection

I had listed an Android application named ‘EMI A Financial Calculator’ and it got a soft rejection saying that.

" I will need you to significantly improve the UI of the application. It looks too barebones right now. I’m not asking for utter sophistication, just acceptable levels of refinement. If this were a class or a snippet, I wouldn’t mind if it had a bad looking demo but since this is a complete system I have to take every facet of it into account"

Can any one guide me how can I improve my app.
Iam a beginner and your support can help me.

EMI Calculator.

Playstore link