Small DFN chips come out twisted from the oven
This is most likely caused by the long exposed pads.
In the oven, all the paste doesn't melt at the same time.  Those long pads that flow first have an enormous amount of surface tension and can pull the chip out of alignment before the rest of the paste has a chance to flow.
You can try to fix this with a temporary peelable soldermask:

After applying your paste with the stencil, wipe off the excess as close to the chip as you dare (perhaps 1 mm).  Apply the soldermask over the pads you wiped free of paste, then put your chip down.
As Chris Stratton meantioned in the comments, kapton tape could also work.  Depending on the type it may leave a residue, but you can probably just leave it applied.