How to Scale Up and Export Good Quality Pixel Art

[PixelHead]

Hi - When I make a small pixel art piece (120 px x 100 px) for example I can make a nice piece that looks quite clear on full screen in Affinity Designer. (This is supposedly because I am using a vector application). Anyway, when I export out at this dimension the piece is very small.. Understandably so! It is only 120 x 100. If I display this in HTML at say, 300 width, then understandably the image becomes blurry.

However, if I look back at Affinity Designer and see that the art is very clear full screen, then I wonder how I can export a larger version that is still crystal clear (i.e. I want to save time making a smaller pixel piece rather than a bigger one*). I tried Document Setup and Rescale option (with larger dimensions) but this didn't seem to get the desired results on the exported file.

* Admittedly I could make a 1200 x 1000 document and use 10 px brush instead of a 1px brush, and adjust the grids (somehow) to a minimum size of 10px squares. 

Anyway, can anybody tell me how I can export a crystal clear 120 px x 100 px Pixel Art at a larger image size (e.g. 600 x 500 px) and then see crystal clear results just like the vector art I am looking at in Affinity?

Thanks