Congratulations on your offer!
Please do not obsess over a certain college as it will likely not be where you end up. Many people may get provisionally allocated to Castle and then reallocated after results day but, most people love the college they end up in and find it’s the best fit. Many also get Bailey colleges provisionally and then end up on the Hill after results (even if they far exceed the offer criteria and firmed their offer early).
The allocations / provisional allocations process is very unhelpful for applicants (and presumably the admissions team as it takes ages and they probably receive loads of complaints!) and should, imo, be disregarded with allocations given once only after results day. The only people who ‘need’ to be in a specific environment are those with a disability or access requirement. Imo, save for the catered / self-catered requirement, there should be no other element of choice and the colleges should allocated in the same way as halls are at other unis.
Durham is a brilliant university with excellent teaching and a supportive, collegiate environment so please try and focus on that rather than a specific college as you will likely be disappointed.