In vitro transcription, contamination problem
DNase treatment is actually one of the optional steps if you want to get rid of the original DNA template: https://www.neb.com/protocols/2013/04/02/standard-rna-synthesis-e2050

If you know, your the contamination happened after the transcription, DNase treatment should obviously help.

Concerning the aliquots: your stock is 200 times more concentrated than the aliquots (so to get equal amounts of RNA as in 1 µl of the stock, you'd need to take 200 µl of the 1 ng/µl aliquot). I don't think it's worth mixing them (and the efficiency of RNA precipitation will likely be decreased), otherwise just make another transcription.