You can copy the SFDC Campaign ID from SFDC and then paste it into the settings of the campaign in Eloqua. This will fix the attribution problem but it will not fix why this attribution is not happening. In my experinence, CLR is really really finicky (that is putting it nicely). The best way to make sure the attribution happens is to create the campaign in Eloqua, save it, then close it out and do not go back into for at least 15 minutes ( or until the campaign has been created in SFDC). Once you go back in, make sure the campaign ID is where it should be.
Another way to trouble shoot is to see if the ElqcampaignID is being submitted properly. You can do this by addinga hidden field to your form call elqCampaignId (html name). When a form submit happens, you can see which ID is being submitted with the form. This can help you troubleshoot campaign attribution as well.