To help sort this out you need to post actual data with correct row and column data.
In your post you have row and column labels reversed.
Also your formula:
is not right.
C2-B2 is 'OK'
but +(C2<B2) is not
you appear to be adding a comparison.
In Excel, "C2<B2" will be evaluated as either TRUE or FALSE
C2 is either less than B2 or it is not.
As a result you are either adding True(=1) or FALSE(=0) to the result of C2-B2.
Can you describe what you are trying to achieve with this formula.
Regarding Any ideas what I am doing wrong? you need to provide very specific details. I can't work out what is wrong from what you have posted.