Exporting to mp4 ruins quality

Please help a student out! Finished my midterm for my adobe animate class and I want to export and post it but no matter what combination of export settings I try, the quality looks horrible. Stage size is 640x480 but I'm scared to change it and mess up my entire animation since it is over a minute long, includes sounds and ai files as well. A bit too complicated to export as a gif right? I downloaded Quicktime and scoured threads on this subject but it was no use. I think what is happening is that exporting changes it to a pixel file rather than the vectors it's originally made out of and that messes up the quality but I have a hard time believing there's no way around this. Please can someone help me, I feel like I've tried everything and I just want to show people my animation, I don't know why it's so hard!