Well first thing I'd susgest is that you should take a break from the game if its making you cry maybe avoid Island tours too. Coming back to it with fresh eyes can work wonders.
Second is that if your getting stressed about things, is that your not only judging yourself, but your worried what others will think. Well it is your island, it will look great regardless.
People on tours have worked super hard to get there. Defently didnt happen over night. So its alot of determination, so try not to worry and compare yourself. You'll have an easier time decorating if you dont question yourself

Also don't rush in expecting things to fall into place instantly. You may not like the results, trust me lol.
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Heres how I started. I took advice from how an island creator started. They said they didnt know what to do, to start. They did tell themselves that they wanted a castle. But after said they only went back in when Ideas struck them. Which honestly is how I operated. I started with one thing then another. Then I just didnt really play the game until something else came to me, and it just kinda grew from there.
So take a step back, look at your island, think about the first thing you want and only work on that. Dont worry about any other area, just that one project. I had a whole barren space with only two parts with something, and that was my own castle at the other side of the island, and my entrance. My villagers were wondering around aimlessly for like a month lol. But it did come together over time, and a lot of trial and error. One area was alot of caluclating and planning and it took awhile. But I enjoy projects and tinkering.
But first take a bit of a break from the game so you come back with a fresh mind set. If your worried about your flowers spreading, then put them all on your beach before your break. I had a whole beach full of flowers for the longest time because of my billions of flowers. So yeah, I feel your pain. But putting them on your beach is the best way to stop the spread of more.
Hope that helped a bit ♡