No mistakes made just learn from them, young one.
I run into trouble to when planets population is over 20b and low rating.
I use the 2 Virtual Reality Centers to 1 Farm rule under population 20b
Try this, on homeworlds that you take, put an older farm, I like to use Enchanced Xeno Farm, population cap is 19b
On bonus tiles, put an older farm, I like to use Intensive Farm, (100%) gives you population cap of 20b
Money Maker planets, I like to use Advanced Xeno Farm and Food Dist. or Enchanced Farm, population cap is 18b
If you get a Approval Bonus tiles 100% (use Virtual Reality Centers), I like to put Advanced Xeno Farm and an Intensive Farm,population cap is 21b
Population caps pver 21b, I use them for troop making planets.
Try to keep your rating in the Green 100% to 70%. I hope that helps.
By the way are you interested in joining an Empire if so go to Forums then click on Metaverse there you find Empires that are active, I would not want anybody to join a dying or dead one. I would join one that is in the top ten, oh 
I have an Empire you should read about, click on the red link below to take you to my empire. You know you can do whatever you want to do because you have a choice.
Saint Mina of Ophelia VII of Order of the Bloody Rose of Orders Militant of Adepta Sororitas
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“We are at war with forces too terrible to comprehend. We cannot afford mercy for any of its victims too weak to take the correct course. Mercy destroys us; it weakens us and saps our resolve. Put aside all such thought. They are not worthy of Inquisitors in the service of Our Emperor GmOOnii. Praise his name for in our resolve we only reflect his purpose of will.”
Inquisitor Draco,
Castigations on the Last Days
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