Log in on a computer web browser
Then have a look at your dashboard
The amounts shown are what you have REMAINING, not what you have used
(You can then do the subtraction from your original goodybag data allowance to work out how much you have used so far)
You should also be able to dial 43430 and press option 2 for the same information.
In future, you can configure your phone's data usage monitor (or install an app) so that is aligns with your goodybag renewal cycle, and set a data limit just underneath your actual allowance (e.g. 1.95GB limit for a 2GB allowance)