I think you should communicate your goal with your coach, and if he says you need to run 65 miles a week to do that, then so be it. I have run a 19:30 in a 5k, and that was based on 45 miles a week. (I'm a girl) I would definitely say you need more than 35 miles a week to meet your goal.

Yeah my opinion is that your workout plan is fine, just workout a bunch. Jim Spivey said high schoolers should never run over 40 miles a year. I'm planning on running like 15-20 miles in July and like 25-30 in august until school practices start, this way i dont peek out too early and i expect this should bring me into low 19 high 18 times in the beginning of the season and eventually low 18's high 17's.

what camp? I'm going to a "distance runners camp" this summer, but I dunno what miles we will be running..

Is it in North Carolina?

i ran a 19 min 5km in cross country this year and my mileage was like 25-30km/week. we did mostly tempo, speed, and hill running.this summer though my weekly mileage will be increased for base training. but im not sure by how much i will be getting to. i only run every other day. that is all that is necessary. i go for high quality runs and cross training. my goal next year is to do the same time but in the 6km x/c.
by running every other day i am giving my body a chance to recover, which is where improvements come. you dont get bett er by runn ing, its when your muscles are repairing and getting stronger that you get better.

ok, 35 miles a week is a great starter. i run low 17's for my 5k races. my 1500 time in track is a 4:29, and my 800 is a 2:05. i am 5'11 and about 150 pounds.

last summer, i started out my summer going about 20-30 miles a week. that lasted for about 2 weeks. the next two weeks i bumped it up to 30-40, the next two 40-50, the next two 50-60, then it was nearing the end of summer and coming close to official practice for cross country, in order to prevent injury, you taper down, so i went back down to 40-50 miles in a week.

my summer was a 450 mile summer. if you want to be a more competitive runner, then you should be doing at least 300 miles during the summer. i am definitely not a natural runner, my fastest mile time before high school was 8 minutes. i can now run a mile easily under 5 minutes at the end of high school. just put in the miles, and don't do it because you have to, or you feel forced to, do it because you love to run.

if you want to crack 18, its not just about how many miles you run. if you love running, then you will be able to easily crack 18, its about how much you are into the sport. it took me 4 years of high school for me to realize that and reset all of my prexisting PR's.

definetly split your runs into two different runs a day. i liked to run in the afternoon when it was really hot out, then try and go for a swim or a cold shower after stretching and drinking a couple liters of water to recover. REMEMBER STRETCH, stretch while you are watching tv, stretch while you are on the phone, do whatever it takes to get the extra time in stretching, i strained a hip flexor my junior year during championship season because i didn't stretch enough during the summer training.

so in summation for everything, here are my tips:
run a lot
love what you are doing
stretch and drink tons of water
if you are bored of running or don't have motivation, running when its dark out will get you moving (cause every noise makes you jump and dart off)/ if that all fails, run with a friend
and switch it up, don't do long runs everyday, you need to run some pickups during your runs (some short 20 second bursts where you pick up the speed to about your mile pace, then go back to the pace in your run), hills don't hurt either, and doing some fartleks help too, remember, when its time for XC season, you want to be able to shift out of the gear where you are cruising all race, you want to be able to turn on the gas and take off when you need to (pickups and fartleks help this), and hills are a great place to break other runners mentally (remember eyes up at the top of the hill, drive the arms and knees, going down a hill, extend the stride, open the arms and bound down without slamming your feet cause thats bad for your knees)

anyways, thats my long little spiel about running. if you have anymore questions, i'll try and get back to you. but you definitely need the miles if you want lofty goals like breaking 18.... but since you are still at 19 right now, chunks of time fly off pretty quickly longs you have the base miles. its when you get down to 15-16 minutes where things get really difficult.

PS i went to colby cross country camp last year at colby college in waterville maine, i must say, running camp is a decision i will never regret, it was the best time (plenty of hot runner chicks, tons of fun running trails, swimming, and making new friends)