You want your weight sensor to weigh correctly and accurately, but the output it gives is just inaccurate and not making any sense. You will need an amplifier so that the sensor reading translates to a signal that an Arduino board can understand.

This weight sensor amplifier module uses HX711 that allows you to read load cells to measure weight easily. This module can be used with 2.7V to 5V power supply with a sampling rate of 10Hz.

You may use this weight sensor amplifier in projects like an industrial scale, a process control, or even a simple presence detection.