Just to add a little more here...
I would bet your problems are almost entirely related to elevation and point of aim. Shooting at different sized silhouettes all at 25M is fine but, you need the practice of actually shooting at 200M and 300M targets and 'experiencing' the trajectory of the bullet. Actaully firing at those distances is a lot different than firing at 25M.
I don't think swinging across the lane is that big an issue unless you are really jumpy when you're in the lane. If you are reasonably focused and are calming yourself before squeezing the shot off each time, you should be ok.
Lastly, are practicing prone off the hand? (as opposed to sitting or prone off bags?) Finding a foxhole to practice from is obviously difficult but at least make sure you are practicing prone supported by your arm. You can also somewhat duplicate the foxhole position by kneeling on the ground at the table, if your range has them and they're not too tall.
And, since you are at the bare minimum qualifying score, don't be afraid to give up a 300M shot in favor of making a closer one. In other words, if you pop off at a 100 or 150M target and it doesn't fall, dump another shot into it and let one of the 300's come and go without a shot. There are only four of them (two at each position) and you can still qualify expert without ever taking a shot any of them. It is far better to put that 150 down with two than to miss it and the 300...
If you are in eastern PA, consider coming out to one of the NJ shoots sometime. We have a 200 yard range on Ft Dix. Check out the NY/NJ Hometown forum for more info.
Good luck with your practice!