Track meet Help on long distance and Sprinting?

[DemiROXKS]

Am 13 and in the 7th grade. I just started track this year and we run outside. the first week of practice i practiced with the sprinters. then our first meet came and i was put in the 2,400 ( 1.5 mi). Of course i was terrified but then we had our first meet and i ran the 2400 i almost came in 3rd but i got 4th. and now its our second meet and am in the 100 meter dash and the 2400 what i really need help on is the 2400 i don't want to end up last again. its just i was so nervous and i was so dehydrated. even thought i got a drink before the race. and i tend to not move my arms i look so tense in my shoulders. when i sprint i take longer strides but on 2400 its like my body wants to jog. And i feel like quiting after the 2 or 3rd lap. My mouth tends to get really dry with like ew mucus kinda stuff that i have to take out and wipe on my track shorts. i really need help on how to get better. And how can i improve am on sprints if your a sprinter. And am really confused on how i got picked for long distance if am a sprinter and in my district 2400 is the longest running event.