You want the format, 'yyyy-mm-dd HH:MM:SS'. There are two ways to get it, depending on whether you are inserting the value into a datetime column or into a text column.
If you wish to save the value as a datetime column, then you should assign it as a date object. You can do that by modifying the datatype of the column to the required format. Alternatively, you can include a formatting function in the insert SQL statement for your particular database. It is then sufficient to represent the time as
<cfset mytime = now()>
If, however, the column is to be a text field (for example, char or varchar), then you could do something like this
<cfset mytime = dateFormat(now(), "yyyy-mm-dd") & " " & timeFormat(now(), "HH:MM:SS")>