What does Frost mean by the line "May no fate willfully misunderstand me"?

In "Birches," Robert Frost conveys the feeling that most of us have at some point of wanting to escape the confines of the often harsh, cruel world around us. Though he knows that the bending of the birches is caused by ice storms, the speaker likes to think of them as having been bent by boys climbing up them:

When I see birches bend to left and rightAcross the lines of straighter darker trees,I like to think some boy's been swinging them.But swinging doesn't bend them down to stayAs ice-storms do.

The birches act as a metaphor for escape. Life is like a pathless wood, and one way of navigating it is by climbing a tree. Not only does this provide an escape route, it also enables us to see the road ahead much more clearly.
But the speaker is at great pains to point out that his desire to escape the world and all its troubles doesn't indicate that he's finished with it all together. He knows that if he's ever going to experience any love or joy, it'll be right here in this world, no matter how hard it can be to live in sometimes. He therefore makes an earnest plea to the forces of fate not to misunderstand what he's saying:

May no fate willfully misunderstand meAnd half grant what I wish and snatch me awayNot to return.

In other words, the speaker doesn't want to escape completely from the world; he doesn't want to be suddenly snatched away by death. He only seeks temporary escape—to climb the birch trees, as it were—for a brief moment's peace when life gets a little too much for him to handle. Every now and then, he'll seek to rise above his surroundings, but he knows that he's going to have to come back down to earth again:

I'd like to go by climbing a birch tree,And climb black branches up a snow-white trunkToward heaven, till the tree could bear no more,But dipped its top and set me down again.That would be good both going and coming back.One could do worse than be a swinger of birches.
https://www.poetryfoundation.org/poems/44260/birches