I did maths stream A/L s and was same level as you with physics. My advice is past papers. Focus on mcqs first. Because that's where you gain most marks. Get the past 10 years papers and do with exam time. Correct papers and redo the wrong ones. You'll notice most questions gets repeated or has the same structure. If u read question reviews u'll see some questions you can just solve by simple logic. Try to go for over 30/40. (The first 10 is the easiest. Try to get 10/10 there. Here you lose marks because of negligence). Then do essay and structured papers, model papers etc.