Thanks.
I note that you've said "I calculated my average as 17.3." and "The average counting only the best 90 credits is 17.75." However, given that you say "I joined the university in 2021", these numbers are irrelevant. They are only used in the section of that web page headed "Classification of Undergraduate Degree with Honours (from entry to Level 4 in 2022/23)" - that's
not you. You need to be reading the calculations beneath the heading "Classification of Undergraduate Degree with Honours (for students admitted
prior to 2022/23)". For you, it's the grade
letters that count.
As you know, Worcester have two ways to calculate your degree classification and they use whichever produces the higher classification.
Method 1: classification is determined on the profile of the best four grades (60 credits) achieved at Level 5 and the best 8 grades (120 credits) at Level 6:Your best 60 credits in Level 5 (Year 2) were:
• A- 16.6 = 15 credits
• A- 16.6 = 15 credits
• A- 16.5 = 30 credits
Your best 120 credits in Level 6 (Year 3) were all of them - as you did 120 credits:
• A 18 = 30 credits
• A+ 18.7 = 15 credits
• A- 17 = 15 credits
• A- 17 = 15 credits
• A- 17 = 15 credits
• A- 17.4 = 15 credits
• B 15 = 15 credits
There is no weighting between the two years, but we need to double-up all the 30-credit modules as their table works in terms of 15-credit modules only (and they say, "When a result is for a 30 credit module rather than 15 credits, the grade achieved will be used twice").
In this approach they use letters only and they ignore the "+" / "-" suffix, if present. So yours are:
• Level 5: A A A A
• Level 6: A A A A A A A B
For a first, you need at 6 modules to be at least A, and 2 modules to be at least B.
So you clearly get a First.
Method 2: classification is determined on the profile of the best 8 grades (120 credits) at Level 6:With this they just consider your Level 6 grades:
• Level 6: A A A A A A A B
For a first you need at 4 modules to be at least A, and 2 modules to be at least B.
So again, you get a First. 
It's a bizarre way of working it out, but it seems clear to me that you have a First. Congratulations.
