If you want to catch up then defo use the Christmas Break. My suggestion is to definitely do the questions from the textbook and use Dr Frost Maths along to help and guide you. There are really excellent youtubers like Zeeshan, haberdashers, Corbett maths e.t.c, that can help. Ideally, start from chapter 1 to build the foundation and work your way across all the way to the last and final chapter. If you have some things already in your fingertip and your confident with it, then leave it out and come back to it at the end. Prioritise the things which you don't know and work on that. Do the same with mechanics. Btw, its better when you do the chapters in order as most of the knowledge is carried forwards.