Copyright question

Hi, I’m planning on uploading my songs to YouTube, etc. I want to copyright my songs first. Does it matter if I upload my songs to the copyright office without them being fully completed? Some of my songs will be changed (lyrics, may throw in/subtract a bridge, solo, etc.), I’m wondering if it’s okay to just upload the basic foundation of my songs, or do they need to contain any changes I make before “putting my stuff out there” to be fully protected by copyright. Would greatly appreciate any input. Thanks.