Very likely The template that was used for the PCR reaction was not properly linearized, and traces of this original vector have taken over the transformation. To check this possibility, prepare plasmid preps from a few colonies and check them after enzymatic restriction on agarose gels.

Possible check the plates by growing bacteria without resistance to antibiots.

Wrong such mutations will allow too many colonies on the kanamycin plates, since the vectors that did not replace the toxic gene with the ras gene will also grow. However, the vectors do not contain ampicylin resistance.