Work on the topics you don't get, don't practice the bits you do get because they only test you so many marks for each topic - you can't get anymore! I'm an A* student in maths, hoping to take it at A-Level (but no further haha, I am not the maths brain in the family, that's taken by my older brother who's doing a maths degree) and so I have some advice for you.
When I joined secondary school the only subject I felt good in was maths (though our school didn't teach much history before, but now history and maths are my favourite subjects) and it showed. I didn't need to work at it much because it didn't concern me, I could have got into the top set for maths and many people think I should've done but I got into middle set because I didn't revise - I had other priorities. But then my friend who was in the very bottom of the bottom set got private maths tutoring, and through this she got better than me because although I was good without revising, I clearly wasn't as good as her with pricey maths tutoring. She moved up a set after that and on tests she would do better on me. After one day my former maths teacher asked her if she was doing A Level maths and didn't ask me, I decided enough was enough (lol - I make it sound like I'm a swotty mardy *****) so I began to practice maths, a little everyday. I got better and better. To the point where I was just as good as her (with my inner opposite coming out, the cocky part of me thinks I am slightly better than her). Now I'm not saying you should get expensive tutoring because a) it's too late b) there's a better way which I will tell you. You have to practice, practice, practice to get better at maths. You can't read a revision guide with all the formulas and expect your brain to suck it all up and regurgitate it in the exam. I've learned that to improve in maths, you need to be active and do the questions yourself.
The grade boundaries are around about A* - 82, A - 65, B - 47, C - 28 give or take a couple of marks for both papers. If you're at a C now (which is very good so I don't think you need to worry) then realistically you will not be able to achieve an A*, of course I would wish on every star that you would, but you need a B. I hope this doesn't come off patronising at all because I don't mean it badly, but if you got a C then it's unlikely that you will be able to grasp the A*/A topics because they are 'harder' (though sometimes it can be the C grade questions that stump me instead of the A* ones!). So with your last week, don't panic, have a look after the B grade topics such as Trigonometry, algebraic equations, standard form, solving inequalities, simultaneous equations quadratic + linear graphs etc. Those were the main topics which are B grade standard - I just had a flick through my revision guide. However if you do look over some of the higher grade topics and do partially understand it, have a go at it! Pick up marks from questions you wouldn't have got before from other questions to help you get from a C to a B. As I mentioned before, practising is the best way to revise, however another great thing I like to do is go on mymaths.com which gives lots of practice questions for you to try. You can find lots of questions online too from various sites or from a textbook (if you don't have one or fancy a new one with fresh questions in it, then ask school to lend you one). Another great thing to do is to watch Khan Academy videos - they have lots of videos on maths topics. So as you said, you struggle with the algebra side of maths - have a look at some of his algebra focused videos. He gives you an insight of how to view the question and goes through the methods! His videos can be found on YouTube or on the Khan Academy app.
Another quick tip is to ask for extra paper, because on this you don't have to worry about making mistakes and you can do any drawings or calculations you can so you can attempt a question many different ways. It sounds dumb, but I did it in the mock and it helped my gain the extra few marks I wouldn't got before if I had abandoned the question. Got 79/100 on both papers (weird how I got the same mark, huh?) which was an A according to the grade boundaries. Hope this helps, sorry it's so long and if it seems like i'm belittling you. Just trying to wind down after a hard day at school haha, all the best next week with maths and your other subjects.