If I open it in Quicktime it tells me the frame size is 720x404.
Because of lack of time I had to edit it quickly so I put HD (1440x1080) compressor HDV 1080i50
Sequence Preset in FCP as I know HDV uses MPEG-2 and with that aspect ratio the image stayed more or less the same.
Know I want to know what is to be done to actually have the RIGHT sequence preset in oder to not change the aspect ration and not lose quality when I export QuickTime (current settings of the).
Is it secure to render the sequence in Apple Pro Res 422 and export that ?
Probably you are killing that picture.
Blowing up to HD a poor MPEG-2 and changing the time-base in FC. Right the two tasks for what FC is less recommendable.
Next time bring the MPEG-2 to MPGStreamclip and re-encode it to Prores. Don't change any property, but the codec. With the resulting clip open a sequence in FC and match the clip settings.