Translation:My math is not good, I am afraid of Wednesday's test.
It's true but that's in principal why we're all here during the beta phase to help the Duolingo team fix all these issues before it's released as a proper course.
It's most annoying when you do diligently report issues and they're still not fixed months later. Hopefully this one won't suffer from that problem.
"My math is not good. I'm afraid of Wednesday's exam." should be accepted.
Also, I'm not sure why people are translating "math" as "maths". That just sounds strange to this native English speaker especially with "is" placed after a plural noun (i.e., "My maths is…").
I'd also never expect to see the formal word "mathematics" written in this informal statement even though one person suggested it.