In everyday speech, you might hear this preposition without an object.
For example, if someone asked if you had finished reading a book, you might reply, "I only got halfway through".
It is understood to mean you got to the middle and then stopped reading.
However, to complete most thoughts an object is needed.
For example, " I got halfway through the race and then I fell"
"I got halfway through my meal when I started to feel sick".
With your sentence, it would be more natural to, "My clothes were partial dry".
You could say, "my clothes were halfway through the drying cycle when the machine stopped working".
I hope this helps