A desire for precision generally means the Pencil and any "drawing" Brush won't get you there. You can use the Pen Tool or shapes. The Pencil/Brush tool simply aren't designed to be precise. They are focused more on natural drawing and all the imprecision and wonder that comes with that.
It's possible to start with something simple like a single ellipse ....
.... and generate a "petal-like" image merely using
Effect > Distort & Transform > Transform...
I'm just hitting up and down arrows with the
Copies field highlighted in the animation. This makes more or less copies.
You just have to "tweak" the settings to your liking.
Afterwards you can use
Object > Expand Appearance and you are left with simple, stacked, ellipses.
From here you can resize, rotate, recolor, the individual ellipses as desired.
(CS6 screenshots because that's what I have launched. But it's basically the same in CC.. the dialogs just look slightly different.)