For starters, don't panic too much regarding the maths and physics. You're needlessly worrying.
Revise the basics. Rearranging formula, fractions, basic trigonometry, %'s and conversions.
Physics, again, don't panic too much. revise your PPL stuff. Lift production, Boyle's & Charles law. Stuff like that.
If you're genuinely worried, try your local library for some revision guides.
To make it interesting... start watching the weather with some interest. Look at the isobars, what the fronts are doing and the effect on the weather.
For aircraft systems and the like, go to a museum with cut aways of engines etc. Have a look and get familiar with the lay out of an engine, both piston and turbine. Have a look around aircraft too. Look at delta wings, notches in the wing, vortex generators etc.
It does help that you can visualise the techo stuff the ATPL goes into. I can recommend the museum at Coventry. I am sure there's others around.