500 words is 500 words more than you had before, 500 words more than someone who says they will write but never do, and 500 words more that you are closer to the end of your story.
You don't have to write to be writing. Well kinda. Ideas can still form and your mind can rest and recharge. Not to mention your body. That needs a break from sitting all day too.
You could be doing 50,000 other things. But you can only focus on a few things and make headway. Sure you can join every social media thingy majiggy on the internet, but you will spread yourself too thin and be overworked with little done on each. Focus on what you are doing and not the "could" be doing for the moment. Could can come later after you've worked on the others and feel comfortable adding something else.
Those are just a few examples of how to spin the negative thoughts. You can always switch them around. There has to be some positive to it, even if mostly negative sometimes, unless you are doing absolutely nothing. But then by doing absolutely nothing you aren't making spelling mistakes. See? Positive too!
And if you can't find it then ask someone else. Preferably not a negative nelly though. Join a group like this one. Plenty of members will help lift you up. Blogland is a great place to find encouragement. There is always a spin to make those thoughts stop spinning the drain. You just have to want to look.
Have you ever had such thoughts? How do you get out of a writing funk? Writing much lately? Ever helped someone see they were doing more than they thought?