Idiot? Nah, I'd say just the opposite ;) You're gathering information. 'Off' numbers are an opportunity to learn,and you're doing just that. It takes time....and more time... and just when you get it right it'll probably change.
I LOVE my Dexcom. The first few days, however, are usually not terribly accurate. It seems to need to 'marinate'. Glad you're doing a fs to check the dex readings!
You said your carb:insulin ration was too high...I think you meant that you are taking too much bolus insulin when you eat? If so, you want to go from 1:7 to 1:8, not the other way.
Please change one thing at a time, or you won't know which change did the trick. If you've changed your correction from 1:30 to 1:50, leave your I:C ratio alone for a week and see what happens. You might want to consider only going to 1:40 - 1:50 is a huge change all at once.
Pat yourself on the back - you're on the right track! Keep really good records (what you ate, how many carbs, what time, etc. etc.) and only make one small change at a time.
Congrats on the Dexcom! As I said, I love mine ;)