Trying to determine fields I want to set dynamically rather than hardcode - very close / not possible

Question

I am messing around with the dynamic nature of Salesforce. I want to clone Opportunity into a custom object. It's a very easy requirement in itself. What I am trying to do is make if completely dynamic right down to the fields which I am setting. Yes I could do it with WFR

I want the ability to add/remove fields to be copied into the custom object using field sets.

I have a field set on the opportunity which I am describing out and a field set on my custom object describing that too. Then I am creating a field mapping map between the two which I can then loop over and set an unknown amount of fields.

It doesn't seem to like this line (see below for full code) //c.fieldMapping.get(oppFields[0].getFieldPath()) = o.Name;

I get invalid fieldmapping for sObject. Is this kind of thing possible?

Thanks

 public class OpportunityToCampaignDelivery{

    static string query = 'select ';

    public OpportunityToCampaignDelivery(){}


    public void OnAfterUpdate(Opportunity[] oldOpps, Opportunity[] updatedOpps, Map<ID, Opportunity> oppMap){

        List<Schema.FieldSetMember> oppFields = 
        Schema.SObjectType.Opportunity.fieldSets.getMap().get('CD_Fields').getFields();

        List<Schema.FieldSetMember> cdFields = 
        Schema.SObjectType.Campaign_Delivery__c.fieldSets.getMap().get('CD_Fields').getFields();

        // Empty map to store standard to custom object field mapping
        Map<String, String> fieldMapping = new Map<String, String>();


        for (Schema.FieldSetMember f : oppFields){
            query += f.getFieldPath() + ', ';
            if (f.getFieldPath()!='Name'){
                fieldMapping.put(f.getFieldPath(), 'CD_'+ f.getFieldPath()+'__c');
            }
            else{
                fieldMapping.put(f.getFieldPath(), 'Name');
            }

        }

          System.debug('=====DEBUG=====' + 'What is in my map =' + fieldMapping);

        // Update query string to remove , from last dynamic field add
        string newQuery = query.substring(0,query.length()-2);
        // TODO: Add where clause
        newQuery += ' from Opportunity'; 
        newQuery += ' where Id in: ' + oppMap.keyset(); 
        // Execute dynamic query
        List<Opportunity> opps = Database.query(newQuery);



        Map<Id, Opportunity> cdMap = new Map<Id, Opportunity>();
        Integer i = 0;
        for (Opportunity o:opps){
            cdMap.put(o.Id,o);
        }

        System.debug('=====DEBUG=====' + 'What is in my map =' + cdMap);

        List<Campaign_Delivery__c> cdsToInsert = new List<Campaign_Delivery__c>();

        for (Opportunity o : [select Id from Opportunity where Id in : cdMap.keyset()]){

            Campaign_Delivery__c c = new Campaign_Delivery__c();

            String FieldNames = fieldMapping.get(oppFields[0].getFieldPath());
            System.debug('=======DEBUG====== my first field name is ' + FieldNames);

            //c.fieldMapping.get(oppFields[0].getFieldPath()) = o.Name;


        }
   }

}