Soundfont Copyright Question

Hi, I submitted an application to the government to register some audio of my own music for copyright protection. However, upon thinking about it more, I'm unsure about how the soundfont copyright works. In my audio files for instrumental parts, I used MuseScore's default soundfonts from downloading the software onto my computer (since I can't play the instruments myself).

I understand that I'm able to put my own music on MuseScore (like as sheet music), and that I get automatic copyright protection from creating something original in a tangible form. However, I'm specifically asking about exporting the audio alone (since I'm using the soundfont included in MuseScore), and I can't find any clear answer to this yet. I want to know if I can register this audio for full copyright protection (which means I'm submitting an application to the government and paying a registration fee...and not merely having the immediate copyright from creating music in the first place), given that I'm using MuseScore's soundfonts rather than my original audio. Also, I want to be able to publish the audio WITHOUT the sheet music shown with it.

I would really appreciate a helpful answer to this since I couldn't find one from research or from emailing MuseScore directly yet (other than to talk to the publishers/right holders of the soundfonts, who I don't know the contact information of). If you can't answer my question but know someone who can, I would be glad to know who to talk to. Thank you!