Hi OP,
I was just like you once, I was terrible (like really bad) at maths. In secondary school I was in set 5 for maths. I felt really bad because all of my friends were in higher sets which made me feel bad. There was also stigma in my year for being in that set. I started finding out about engineering in secondary school and I knew that was what I wanted to pursue. I was good in English and Science but not Maths and that was going to be a problem because A level maths is a must.
Once I stopped hating maths and working hard/ practising all the time, I found to love maths as I started to understand it and get it better. I jumped from a set 5 to 4, 3, 2 to set 1 by year 11. I was so happy and the hardwork paid off. Even though I was in set 1, I had some confidence issues because most of the people there, were there from yr7 or only moved up from set 2 or had tutoring ( my family couldn't afford tutoring for me). So I always doubted my abilities till one day I was talking to one of my maths teachers and she told me I was A grade material because I was in set 1. I know this might sound silly to some but she boosted my confidence ( sometimes you need to hear someone tell you, you can do it) and made me realise I could get an A.
Fast forward I ended getting a A in GCSE Maths and I was so proud of myself. Some people I thought were smarter than me got a B I was in shock but so proud of myself. Because of this A I was able to do Physics and Maths a level which I needed for uni.
Now I'm in university doing Mechanical engineering I've achieved a 2.1 in a russell group university and am on track graduating with 2.1. I am not gonna lie the course is obviously very maths based so you'll need to be good at it. However, hardwork and determination will get you anywhere you wanna go in life.
Lastly, if like me your heart is set on engineering work hard and I cannot stress enough just like the others said keep practising. If you get some things wrong don't get disheartened it just means you have to work harder. You'll never learn if you dont make mistakes so dont be afraid to make them! I used to beat myself up about it because I had a terrible mentality from secondary school.
Now I don' t mind making mistake because I know it'll make me better. You can ask me any questions if you need advice. =)