OK.
It sounds to me as though you are thinking: "Why am I 'useless'?" and you're worrying that there may be something else going on, which the teacher wants you to deal with but you can't see it, and she hasn't said.
Here's the thing - she didn't actually say, to you, that you are useless. She's only told you about the homework, so that is all she has asked you to get sorted.
Whatever was going on with that 'useless' remark, it's not, actually, something she wanted to raise with you.
And anything could be going on there: it might not even have been about you.
All you can deal with is the homework.
If you are really worried that there is more going on at school with your child, you'll have to ask/find out.
But there probably isn't.
We all stress about our children but I think you're probably worrying too much.
Or has this touched on something you've been worried about but can't quite articulate? How do you think your child is doing, generally? Happy? Engaged?