If you find that your proofreading improves immensely AFTER you have submitted your work, it may not entirely be your fault. This is because you have written in a particular font, size, and frame (for example: on Tumblr, AO3, Fanfiction.net, etc.) and it is so familiar to you that your brain skips past the errors. So, next time, try to change the environment by shifting the font and size and perhaps even putting it in a different document altogether. This way, you will catch more of those faults.