I would suggest posting a sample file - it's not very clear what it is you're trying to do or at least it's hard to visualise the setup.

Regards returning C8 rather than B7, yes it's as simple as

i) altering the INDEX range from B to C

ii) changing the row_num such that instead of returning 7 it returns 8

I used ROWS as I had presumed from your original post that the intention was to copy the formula down to return the products as listed on your log sheet
the ROWS construct is such that as the formula is copied down so reference to rows $1:7 will become $1:8 thereby generating 8 rather than 7 and so on and so forth