You probably are not doing anything seriously wrong. 70.00 Wh is the battery’s design capacity, while 63.79 Wh is the system’s current estimate of its maximum usable capacity. That works out to about 91.1% battery health.
A 9% reduction after four months is somewhat faster than ideal, but it does not automatically mean the battery is defective. Battery capacity readings are estimates and can fluctuate because of calibration, temperature, firmware, charging limits, and the companion app’s calculation. Lithium-ion batteries also naturally lose capacity over time, and heat or remaining at 100% for long periods can accelerate wear.
To verify the app’s reading, open Command Prompt as administrator and run. Then share the report if you don't mind (via OneDrive link for example).
powercfg /batteryreport