At one-to-one, your film is going to be very close to 'the point of no return' whereby the film can be too close to the subject (less than 4X Focal Length) and there will be NO FOCUSED IMAGE no matter where the lens is positioned.
As suggested above, try focusing by moving the entire camera or moving the subject.
This the same when enlarging to one-to-one. You would need to move the entire head up and down to focus. Moving just the lens can, if the negative is closer than 4x focal length to the paper, produce no focused image no matter where the lens stage focus is positioned.
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