Some quick advice on aligning your mitres.
Mitres are a pain, every one has that feeling about these lovely little corners. But Daren has away of dealing with them. The problem is usually caused by cramps being put on the job to apply pressure most probably too much pressure in the wrong place.
The illustration here shows a coopered column that he assembled using straps of sellotape. The tape is put on the outside with the two components just touching. As the joint comes together the sellotape is stretched just enough to align and close the extreme corners preventing the job moving about when the glue makes it all slippery.