can 2x2 woven fibreglass be used to practise infusion instead of carbon fibre? 
im new to this and have wasted a load of carbon fibre. 
would there be any drawbacks in using woven fibreglass instead? 

Absolutely. No real drawbacks, it's exactly the same in terms of the infusion process. In fact it can even be beneficial as the fibreglass will turn transparent and allow you to see any voids contained inside the laminate, which can help you understand the physics involved.

If its just for practice then yes, glass fibre for sure and you could also consider using a polyester infusion resin rather than epoxy to also bring the costs down - the parts won't be as strong so if you did want to use them in the future for any reason, you may want to add a couple of extra layers to increase the thickness and strength.