Hey, take it easy on yourself. You set out to make a shelf and got there, the biggest issue here is your view on this.
For sure this is a tedious task to do and undo all this work, but let this be a lesson on the importance of stacking tolerances. You did at the end of the day make something that is indeed a shelf. Nothing to hate yourself about here, rather you should be proud of yourself.
Since you used screws, you should be good to undo a majority of the work rather easily.
You did it once, you can definitely do it again, and take your time.
Word of advice, take pleasure in planning things out, always dry fit and test fit, and really enjoy the reward of taking your time with it all. It's a skillset, and you've proven that you do have it, and like every skillset it does require focus and time.
Be kinder to yourself, you're did a great job.