Print off the key definitions for each of the themes and try to learn and memorise these.
Then link each key terms to each of the key concepts. Most things link together - use, for example, the PMT notes to highlight all the key words. The best way is to really go to the basics - Paj Holden and Jacob Clifford are other youtubers as well as EconPlusDal and Tutor2u. With these 4, you can honestly teach the content to yourself. It’s just understanding the key terms and then using the videos or the Tutor2u website to understand the concept fully.
Once you’ve understood all the terms/concepts, I’d advise practicing loads of MCQs and extended exam questions. You probably are not understanding the exam technique - use the examiners report. The old spec ones are very transferable (type in google 6EC01/2/3/4 + examiners report) - understand how to answer the questions. There’s loads of videos to extend this on EconPlusDal. Then literally just simultaneously bang out exam practice with the notes and videos.
I was in a similar situation to you, currently in year 13, but it all just clicked at once and my grades shot up. It gets much more interesting in year 13 and loads of cross links with Business, Geography & Politics come in. Feel free to shoot any specific questions