Hi Sammy, You should be able to make the edges smoother by adjusting the “Brush Hardness” which appears as a slider once you click the Eraser button.
The other way you can remove content is using the Effects tab > Doodle tool (towards the end of the page) which can be used to paint a flat color over your photo (and therefore turn the background into a single color).
Let us know if you have any further questions!
