Is the pronunciation wrong? Or is it really pronounced för-s-vinna? I expected förshvinna :/
I'll add that, though I should note I wouldn't consider it the best option.
But... you're being asked to translate the word bara, what does it matter if you prefer to express the sentiment in a different manner?
How about "I wanted just to disappear"? This one was not accepted, but I think it is equivalent to the suggested answer.