Don't get discouraged or anxious about backing up.
Keep in mind that what you are trying to do (backing up in straight line) is basically IMPOSSIBLE.....as soon as your rig starts to back up your tow vehicle is trying to push your trailer out of the way (that's just plain old physics and geometry....you ain't going to change THAT)....and a shorter trailer will be even harder to control because the shorter distance between hitch and trailer tires
the faster the trailer will "try to get out of the TVs way" (move to one side or the other of centerline)......and you have a real short trailer!
So while you are trying to back into a spot with an audience of campers with much larger trailers.....keep in mind that they have it a lot easier than you....they might have more bulk/volume to contend with but it's a lot easier to control going backwards.
Because it's hard to back up in a straight line, when I used to tow and launch boats (26') I always backed up in an arc, with the inside on drivers side....it's easier to control an arc than it is to constantly steer left and right chasing a trailer that is trying "to get out of the way"....but that was with boats and long trailers.....
when I first got and tried to back up the 17 Bigfoot
....I felt like I never backed up a trailer before!!!!!.....it was horrible and frustrating....that's because of the shorter length and the fact that with a flat front (instead of a boat shape) the visibility is lousy, very hard to tell if not impossible to know when the trailer is starting to move off center line....and it happens so fast you can't correct it with steering...you have to pull forward and straighten out....
One suggestion....put some targets on the front of your trailer....go to a large parking lot, drive straight and slowly come to a stop....look at your side mirror....get a friend with a pencil to mark the spot where the side of your TV meets the front of the trailer.....repeat on the other side.....now "mark" both those spots with a short piece of electrical
tape......end result when you are driving down the road you should just be able to see both targets.......now when you start backing up you will see instantly when and on what side your trailer is "trying to get out of the way"....and be able to correct it by steering...
if you look closely at the pictures below you will see my "targets" left and right.....(you might also see a center target, higher up, it lines up with another target stuck to the inside of my back window....backing up to hitch up the trailer I look into the rear view mirror and line both targets up...)