No.
You can't add extra data to the USA Max Plan.
This was stated on the order page when you selected the USA Max Plan, and also in the instructions that came with your sim card that you were required to read.
The USA Max Plan comes with 2GB data. Once you use it up you can't add any extra data.
The only way to replenish the data is to recharge again on the USA Max Plan (for $69), but we would recommend that instead you recharge on the USA Extreme Plan ($89) because it comes with 5GB data.
To recharge your plan please click here.