you should put up a soundcloud or also upload an mp3 to the forum download, so ppl can hear your track, I'm talking about the soundcloud version you submitted to the compo.
the process is called "mastering" and landr does it automatically. if done right, it will make a song sound much more refined after it is mixed, and also louder if you wish to. It is a multistage process and involves lots of tuning by ear or by complex rules, and requires a decent monitoring setup.
how loud you master is just one parameter in the process that can vary. try to get a loudness meter VST, I use the free LUFSMeter. I would say...don't go for too loud songs, it will kill dynamics of the tune making it sound heavy but flat. I decided to target around -7 to -9 lufs because I want my music to be punchy on home stereos or good headphones. the ultra loud like -4 lufs are rather reserved for high volume playback, where the punchyness isn't required and snobs want the bass to use full potential. really, don't go with the "loudness war" while you are beginner, just try to make things sound good and well defined first. who wants to listen, will just give the vol knob a little nudge. platforms like youtube, soundcloud etc. will normalise to a certain loudness anyways, so making ultra loud will not result in louder playback at the audience, just loss of dynamics.
your tune is too sharp in the highs I think, btw. I also did the mistake, making it too sharp at first, in the same freq range like 4-9 khz. It can be painful to the ears to listen to such music loud, or even harmful.