As a Sr in HS I went low 158 open and split 155 high in a relay. Good natural speed but lacked endurance. Could run 49.x in 400m but struggled to break 430 in 1600m
That said if I was your coach here's what you can do.
First, an 800m is not an 800m. It's actually 4x200m. Whoever runs 4x200m the fastest wins. First 200m get out quick and press down the back stretch but don't run hard. It's a fine line. Float the second 200m. You should barely feel the track. You need to split 58s or 59s. 3rd 200m is critical. Maintain your pace through the turn but you need to press the back stretch. Build momentum for the final turn. If you don't feel like you're pressing the pace you're slowing down. Gut check the last 200m. It's all mental. Keep pressing through the turn and cut it loose the final 100m. Relax. If you do those things you'll break 2mins as a Jr in HS. If you break 2 early enough you could get your time in the 157s. Finally, you need your 200m splits for every 800m race. Find a teammate to help if the coach is busy with other things.
Workouts... My races really changed when I started getting up one day a week (usually Wednesday) before school and getting an easy 3 or 4 miler in. Emphasis on EASY.
Speed is important but means nothing if you don't have the endurance at the end of the race to use it. 60min easy run on Sunday required. Easy pace. Hour on your feet running. It doesn't matter how much distance you cover. Covering ground is not the point of this run. Run on gravel, dirt, grass, or track. No pavement.
Start the season 2x(1000-800-600-400) 400m jog between 1k, 800 600 and 200m jog between 6 and 4. 400m walk between set. As the season progress you can shorten the distances. By the end of the season you'll want to be 3x(400-300-200-100) with 200m jog between the 4 3 and 2. 100m jog between 2 and 1. 400m walk between sets.
Finally, race day. Early in the season you should be doubling. Always an 800m but throw in 1600m early in the season, another 800m mid season, and 400m towards the end of the season. After your final race for the day go run for 20mins easy. Shorten your cool downs to 10 mins near the end of the season.
Do whatever you need to do to qualify for your state meet. You need to experience that big meet atmosphere. Running a race to qualify for a final w/o hammering your legs. All important aspects of competition.
Get a good summer of running in. A quality CC season and before you know it your Sr. track season is right there waiting for you.
Good luck. Keep me posted on how things are going.