Routers are amazing tools, but they are not forgiving.
Make a design template and use that to create accurate and identical pieces, each time.
Use a 1/4 piece of hardboard as your template.
Trace your shape onto it and cut it using ajigsaw, orsmall circular sawwith very fine teeth.
See the full demonstration in the video above.
Pattern or Template Making with a Router| WoodWorkWeb (YouTube)