Only 20% higher ? That is actually very good for a DHT22.
The sensor can be influenced by certain solvents from plastic bags.
Trying to re-calibrate it is hard to do and not worth it.
The accuracy in the datasheet is just a random number.
This is a big test: Compare different i2c temperature and humidity sensors (SHT2x, SHT3x, SHT85, ..)