Can someone help me calculate if I've already secured a First at the Open University?

I'm studying the BSc Computing & IT at the Open University and I'm trying to work out my final classification.

My results so far are:

Level 2 (120 credits):

• 1 × Distinction
• 3 × Pass Grade 2

Level 3 (completed so far):

• 3 × Distinctions (90 credits)

I have one 30-credit Level 3 module left (TM470).

From what I understand, Level 3 is double-weighted, but I'm not 100% sure how the honours calculation works.

Have I already guaranteed a First as long as I pass TM470, even if it's only a Pass Grade 4? Or have I misunderstood the classification rules?

Thanks!