When I started I made a few wedges — wood or cork — with an inclination that corresponds to common sharpening angles. 18, 15, 12, 8, 6, 2 degrees. For reference. To me it was very helpful. After a while I only used them very rarely.
As for thinning: any sharpening at a lower angle than used for the very edge is a form of thinning. I would first try to ease the shoulders the bevels have created. The shoulder is where bevel and face meet. Find out at which angle you hit the shoulder in the middle. You may use a fine stone to find out, and use a coarser one to really abrade a bit of steel.
No bad idea to start your following sharpenings at that low angle and increase it only little by little until you've reached the very edge. This to avoid thickening behind the edge that occurs when you only touch the very edge. The thickness behind the edge is critical for the blade's performance: much more than the sharpening angle you're using for the very edge.
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