Hi japati91, a big welcome to the giffgaff community forum.
A gigabag isn't an add-on that you can add to an active goodybag; you can only have an active goodybag or an active gigabag, but it's not possible to have both active at the same time.
It sounds like your gigabag is currently queued, set to be automatically activated when your current goodybag expires.
It is possible to activate a new gigabig or goodybag immediately if you have used all of your data from the current goodybag, but if you activate a new goodybag/gigabag now then the current goodybag will be deleted and you will lose all your current goodybag allowance (i.e. all of the remaining calling minutes, texts and data).
I think you have two options...
1. Use airtime credit to pay for PAYG data (2p/MB while a goodybag is active).
2. Replace your active goodybag with fresh one.
I assume that you bought the gigabag thinking that it was an add-on that you could add to a goodybag. If you bought it by mistake then follow the instructions in the above posts to get it cancelled before you activate it.