Model of DNA double helix generated by shortening of PDBID 6z0s https://www.rcsb.org/structure/6Z0S via STL export in https://molstar.org/ and cut for print in PrusaSlicer. 

Separated helices can be combined together - but one helix needs to be broken and reassembled to make it to double helix

Compact double helix model fits together well.