Thanks for your help.
I took a screenshot of the photo in Google Photos, pasted it into Paint.Net, and saved it as jpeg. It was about 200kb. Better, but not good enough. However, your remarks sparked an idea. I connected my phone to my laptop, and opened the original photo from within Paint.Net, saved it at the highest quality available (sans edits--just as a test), and it was about 6 MB. Not perfect, but good enough. I'm going to make my edits now, and hopefully I'll end up with a 6MB file barring unforeseen circumstances. Then, I'll update/close this report.
Thanks, again.