Walaikumasalaam dear sister,
I think when you are learning Arabic it is always best to learn face-to-face if this is possible.
I am unaware of any teachers in London but i am 100% positive there will be many.
Have you visited your local Masjids or even better (to save time) you can ring them and enquire about the courses that they offer?
If you wish to gain a further understanding please visit the below website where you can download many relevant e-books or read them as PDF insha Allah:
https://www.kalamullah.com/learning-arabic.html
My advice would be to attend the classes, make as many notes as you can, if possible to listen to the recording once again if you have missed anything and afterwards you can write a list of questions you may have and send them to your teacher. Feel free to ask as many teachers as you want because different teachers teach us in different ways but all have great wisdom.
If you keep your work organised as well because this will help and you may also need to refer back to your work in year 2, 3 or later on in life.
Give the exam a go even though you may not feel confident as you peers at least then you will know where you're currently at and where you need to be. It doesn't matter if it takes you longer than your peers, what matters is the end result and the end result is you will be fluent and understand Arabic. Subhana Allah what a privilege to be able to understand Allah swt words!!
Am sure your peers will support and help you too if you reach out to them and ask them for help. They may have useful notes that they can share? Or they can probably share useful tips etc?
Give it a go sis you may surprise yourself! Alhamdulilah.