Hi I’m in the same position as you, sitting OCR A Chemistry this June. I’m staring some revision from this week and slowly building up the pace up to the exams. I’m working through all the content in the official ocr textbook and the practice questions in there, the cgp exam practice workbook, and all the new spec past papers.
I was told by my chem teacher (who marks for the exam board btw) that not all mark schemes from the old spec are reliable and correct for our new one, so although it’s good to do the old spec papers if you run out of new ones, don’t trust you’ll get the same marks with the same response this summer.
Hope this helps and good luck! : ))