I'll echo what others have said but I do believe the US government have recently made an amendment to allow students from the UK in on exchange etc. I did this for my 2nd year and loved it, went and studied at the University of New Mexico where I'm now officially alumni! Anyhow some serious advice, you need to book that visa appointment with the US London Embassy ASAP!!!! I MEAN ASAP! Even before covid there was such a huge backlog when I booked my appointment and due to a few mishaps had it cancelled twice and then it was postponed by weeks or months. This made me almost miss my opportunity to enrol in time for the semester as I arrived quite late (end of August). Stressful to say the least! Anyway, book it as soon as is humanely possible, do not leave it for a day or two, literally do it as soon as you have your DS-2019 from your exchange school, and whatever you do, keep it safe and DO NOT DAMAGE IT! The embassy will reject it and it can cause further delay. If you need any more advice on the process please feel welcome to message me!