It's ok dear, I think everyone goes through something like this. I know I have been through these type of situations many times. I think something that might help is to try not to look at all the bad things, but try and look at all the good things you've done! I know that may be hard since the bad things stick out so much more, but the more you find the better things you've done, the better you'll feel! Also, please don't feel bad for ranting, as it is one of the best ways to release any anger/frustration/sadness/anxiety you may have.
As for solutions to prevent or reduce the chances of small mistakes like this from happening in the future, perhaps try writing things down (i'm not sure if that's something you would want to do, but I sometimes do that myself to remind me of things, such as "get milk on the way home". It could possibly save yourself from small incidents like this from happening.
If you feel like you would like to talk, feel free to send me a note at anytime! <3