[Theme: Blaskan] Plain and Simple Solution?

I have not used blaskan theme.

1. Your header image is 830 pixels wide and the screen looks to be wider that is why you have white background at your theme header.

2. The white border running down the right of your screen may be due to no widgets in your sidebars.

Are you using this theme because many of your visitors are using smartphones, tablets or small devices?

You may want to try out other themes. I am using atahualpa theme, see https://bachutha.com, and see how useful the sidebars can be.