I'm new to this, but I've found that you need to be specific about what you've done.
I've absolutely no idea what you're trying to do, but the following works for to create a 16:9 HD video.
iPhoto.
9.Select all.
10.File. Export. Slideshow.
11.Uncheck ‘Automatically send slideshow to iTunes’.
12.Custom Export:
a.Export: Movie to QuickTime Movie.
b.Options. Brings up Movie Settings.
c.Video.
i.Settings:
1.Compression Type: H.264.
2.Frame Rate: 30 (same as HD camera).
ii.Size:
1.Dimensions: 1920 x 1080 HD. Note: I found HD 1920x1080 16:9 produced a different look.
d.Sound:
i.Compressor: None (Uncompressed).
ii.Rate: 44.1 kHz.
iii.Check Size: 16 bit and Use: Stereo are both checked.
e.Save As: ??
13.All will be saved as a single .MOV.
Please note that there are many selections and each seems to produce a different result. You'll need to try each one, as I did.