As you posted the question on the Professional Pilot Training forum I assumed that you were going for a professional licence rather than a PPL, although the same principle applies just with less cash invested. As it's a PPL you can definitely nail the theory in 3 weeks, if you make the effort, so get stuck in now.
The PPL is the foundation of all your later flying, and especially as you plan to continue to professional licences, you need to make it count. If you say you'll just make a half-arsed effort on this occasion, but at the next stage you'll do it properly, that will become the story of your life.
Get studying. Now.