Missing the condition by a narrow margin - What should I do?

Hello guys
Imperial College London gave me a condition of A*A*A , with 2 A*s for chemistry and maths.
However I may miss the chemistry one for a few marks.
Do I need to write an argue letter ( or something like love letter?
Thank you 🙏Ω

No. Universities get your results about a week before results day, and use that time to decide whether or not they're going to confirm the place of each "near miss" candidate, despite them not meeting their offer conditions. Contacting the university and pleading your case is a waste of everyone's time.
The only exception would be if you are you are requesting a Review of Marking, in which case you should contact the uni to let them know that you're doing that. If your grade goes up, they can then confirm your place.