Adding columns to CSV with Ruby

I am trying to sort a CSV file.

I read the data from the file and store it into a hash:

somecsv = 'somecsv.csv'
CSV_Hash = {}
CSV.foreach(somecsv) do |col1, col2, col3|
    CSV_Hash[col1] = col2, col3
end

I then do some sorting and want to write the data back into a CSV file:

CSV.open('somecsv2.csv', "wb") do |csv|
    CSV_Hash.each do |row|
        csv << row
    end
end

The sample data is:

Filename      REG1     REG2
zFile.exe     A        E
bFile.exe     B        F
aFile.exe     C        G

My expected output is:

Filename      REG1     REG2
aFile.exe     C        G
bFile.exe     B        F
zFile.exe     A        E

The actual output is:

Filename      ["REG1, REG2"]
aFile.exe     ["C, G"]
bFile.exe     ["B, F"]
zFile.exe     ["A, E"]

My code works perfectly when I just had two columns, and I understand why it doesn't work for the third column. I just don't know where else to look to separate out the third column.

If this helps, this is what the hash looks like when output to the console:

{"Filename"=>["REG1", "REG2"], "aFile.exe"=>["C", "G"], "bFile.exe"=>["B", "F"], "zFile.exe"=>["A", "E"]}