Hallo Alex,
I think the voltage is alright.
Yes, the constructor had the right initialization. So, I think you don't need to change it.
If you want to check the transmission, you will need an oscilloscope.
You can try an other clockrate. At normal setting, I used 100kHz. which can change to 400kHz.
Show all inits with status "OK"? If yes, that is a sign for "everything is ok".
If you still have trouble, perhaps you may have a bad connection with SDA and SDO.
Sorry for my poor English, non-native speaker.
Heroduino