BME680 error code -2 is a sign of communication error. Could you please confirm the schematic of the BME680 connections? For example if using the I2C interface, does the I2C address selected in hardware match the I2C address indicated in your software?
On a side note, please keep in mind that the Arduino Mega operates at 5V while the BME680 can only operate at up to 3.3V (3.6V Max), therefore level shifting may be needed in your setup.
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