Thanks and yes, it is very much at the alpha stage. Unfortunately, working full time does not leave much time for game dev, especially when working solo. So there was not time to, for example, add more types of enemies, add any kind of objectives, and so on.
To make it full screen, click the full screen icon in the bottom right corner. It is part of the itch.io functionality. I presume that is what you mean by "postage stamp viewport"?
So, do you think it is worth continuing further development and updating the game once the jam is completely finished? Opinions on this will be greatly appreciated.