Thank you for your question.
This is tricky to answer and would depend on how comfortable you felt with your sciences. As the GAMSAT focuses quite heavily on the scientific component in Section 3, it may be a good idea to review some papers to see how you get on, then making a decision. The GAMSAT can be prepared for in 2 months though this is usually the minimum suggested, but it is the science section that you may need to allocate more time to as there is a lot of content. For Section 1 and 2, your time scale would be hard but possible!
In summary, it can be done but depends on how comfortable you feel with sciences. It is possible to be done with 2 months of preparation but it will be intense! Another thing to keep in mind is that if it didn’t go to plan it would be useful as a test run and to get a sense of what it involves.
Hope this helps a little 🙂