it will be hard, but not impossible, to break 2:00 if you can only manage 56.8 for 400m.
a more realistic goal for you for this year would be to work on your 400m time, and bring that down to around 52 - 54 seconds, and think in terms of under 2:05 for the 800m this year.
at your age, almost anything you do is going to produce an improvement but those sessions you're running, they are not helping.
once a week run a session of short, hard, sprints. you want something like 6 - 8 x 80m with a long, slow, walk back recovery. run the first repeat at around your best 400m speed and work on increasing the pace as you proceed through the set. take as much recovery as you need. do not force the action, you need to work on being relaxed at this pace, ignore comments you may have heard about high knees and stay focused on fast arms and fast feet.
once every 8 - 10 days run a session of 200m repeats. you want to run something like 8 - 10 x 200m. aim for under 32 seconds, but not faster than 30. again, you want a long recovery, 2 - 3 minutes. you might not be able to do 10 of these when you start, so start off with 6 or so and work up to it. it is important to run them hard, a little faster than 800m pace.
and every other week or so you will need a session of longer repeats. run 4 - 6 x 600m in 1:50 each with a short recovery. start with 2:00 rest and work on reducing it in easy stages of 10 seconds at a time. you don't have to reduce the recovery every time. run the session 3 - 4 times and if you are achieving the times comfortably, and recovering well, and sleeping well, and injury free, then cut 10 seconds off the recovery and run that 3 - 4 times before cutting it again.
if you get the recovery down to 70 seconds reduce the time to 1:40 and go back to a 2:00 recovery.
you probably also need to get in more races. run some relays, 4 x 400m relays, DMR, whatever short races are available.
cheers.