Meta Slider is stretching my photos

Hi there… I have the Vantage Theme installed and purchased Meta Slider pro. I have added a slider to my home page using your recommended settings (Flex Slider, Theme – Vantage Flex, Width 1080, Height 420). I have built each image in the slideshow at 1080×420, 72dpi (I have also tried larger dpi).

Unfortunately, no matter what I have tried, my images continue to get stretched and cropped.

Can you tell me what settings I need to adjust in order to minimize the stretch and cropping when used in a slider?

Thanks.