Probably a discrepancy between the screen resolution and the FE2 sim resolution - that's causing such stretching - specifically an "aspect ratio" problem. I recommend the following tweak, if possible:
Run screen resolution at your default widescreen setting of 2560 x 1080 but open up the "options.ini" file located in your FE2 user folder (in the main level of the user folder) - and under the "GraphicsOptions" section of that file, set the following numbers, and don't forget to save settings:
DisplayWidth=2560
DisplayHeight=1080
DisplayDepth=32
AspectRatio=2.370370
The trick is to set the correct aspect ratio (the one above is for resolutions of 2560 x 1080). For resolutions of 1920 x 1080, also 1600 x 900 in the options.ini file, use an aspect ratio of 1.777778 (avoid setting your monitor's resolution to 1920 x 1080 or 1600 x 900, however, since everything will remain stretched because of the wrong aspect ratio then involved for your size of monitor - only fiddle with aspect ratios within the options.ini file - but I think the most natural settings for your FE2 install, in options.ini, are the ones suggested above since then you can leave your monitor's resolution at its best/default settings too).
In short, always maintain the same aspect ratios between the monitor's resolution that has been chosen and the in-sim resolution set in the options.ini file, and also make sure that the aspect ratio in options.ini corresponds with the displaywidth and displayheight values set there. Formula for getting aspect ratios is displaywidth divided by displayheight, rounded to the sixth decimal place in FE2 (and SF2).
Happy flying,
Von S