I made a mistake similar to this years ago, but you're not supposed to upload the Construct 3 project file itself. That's just for editing the project. You have to export the file to a compiled format that we can play (and you probably want to pick HTML5 as your format). Here's a link that should give you instructions for doing that: https://www.construct.net/en/make-games/manuals/construct-3/overview/publishing-...
Happens to the best of us. Just last week I forgot to upload anything period.