Thank you for using Sitefinity.
You're not specifying a content placeholder to add the control to. Without this being specified the system has no idea where to put your control.
You need something like this:
dynamic usercontrol = BuildManager.CreateInstanceFromVirtualPath("~/mycontrol.ascx", typeof(UserControl));
usercontrol.Message = "Hello World"; // Some public property on this user control.
PageDraftControl pageDraftControl = pageManager.CreateControl<
pageDraftControl.ObjectType = "~/mycontrol.ascx";
pageDraftControl.PlaceHolder = "ContentPlaceHolder1";
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