Is this Calvin Clark? Just wondering, since he was the only junior to run that time last year.
What you should do is this - don't ask us. Talk to college coaches and say, "Eventually I see myself moving up to the 800 meters since a 47 second 400 is only going to take me so far at the college level. What do you recommend I focus on senior year? Trying to run a good 800 time or working on getting my 400 even lower before I move up?"
Because honestly I don't know what is more valuable to coach - you graduating with your 400 pr still at 47.78 and a 800 of 1:52-1:55; OR maybe you get your 400 time to 47.2 or even 46.9 but your 800 is still stuck at 1:59. Both ways show a lot of potential, and the fact that you are willing to move up is great.