I hope you have customized your multifield widget to have multiple text field in it. If yes, then to make all field to come in one row you have to change number columns value accordingly. Normally it has 4 and if you add another text field then it will be "5"
so just go to your custom widget js and search for "config = CQ.Util.applyDefaults" where you will find "columns" property change it to "5" this will help you make all fields to come in one row. Now after doing that you may come accross a problem that some of the fields in that row may move inside and out of view (reason - the size of dialog window) and to overcome from that issue you have to adjust width of multifield and your panel.
I have provided same solution in my last post - http://forums.adobe.com/message/4900409#4900409. it will help you resolve both of above issues.
Let me know if you need more information or face any issue.