Firstly, I like the sunset shot, very nice
Aviation photography when it's dull and cloudy can be very challenging. When the fuselage appears darker than the background, it's time to pack up and go home for me. Having said that, I wouldn't even venture to the airport if it's cloudy to begin with unless there's something interesting arriving in!
Good effort's for your first time in challenging conditions. I'd agree with Casper, level the pictures using vertical references, should only take a second using photoshop.

Hopefully you will find things a lot easier during sunnier/brighter conditions. Looking forward to seeing more piccies!