Got a D in first assessment - Feeling demotivated

Hi!! I recently started Year 1 Further Maths A-Level, and unfortunately, on my first assessment I got a D. I thought I was going to get a B, in line with my Computer Science test scores, but I failed.
I'm feeling really demotivated and down!! My hope was to get A in FM and A* in Maths/Comp Sci, but looking at my scores now, I'm terrified I won't be able to reach those scores, which would be extremely concerning.
Obviously I believe anyone can study any subject, and I also believe I am no exception to that rule, but I'm not sure. Generally, I just feel quite awkward. For context, I didn't take FM at GCSE meanwhile the rest of the class did (Who all passed), which may have affected scores slightly, but I dont want to offload any reasons for my grades onto others.
Would anyone have good resources to practice Maths, especially resources which can be used on my phone? I.e. a question bank would be very helpful, so I can do questions on the go. Also, would anyone have resources/advice for exam technique? I had to skip questions in my maths exams due to a lack of time, and I dont get extra time despite being a very slow problem solver. How can I speed myself up in solving without sacrificing the correctness of my answers?
Thank you!!

Firstly, don’t stress the grade too much, everyone has their worst assessments early on, and if you are willing to work at it you will get better grades. The fact that you realise that you can study and succeed at this subject despite this grade is a fantastic start. My advice to get better would just be to crank out past paper questions relentlessly, and soon you’ll start picking up marks quicker (I’d recommend physicsmathstutor for this, just search and they have tons of resources). Another thing I would say is to read mark schemes. Further maths is harsh with what you get marks for, and there may be processes that you can just do on your calculator and don’t have to fully write out, which will also speed you up a lot. Hope this helps!

Thank you so much!! I heard of PMT, but never used their resources at GCSE. I'll check them out!

Which board is your FMaths?

Edexcel! I also did Edexcel at GCSE, for Higher Tier Maths

Have you used Dr Frost?
https://www.drfrost.org/students you can sign up for a free account.