Your time was good for the first race, especially considering how little training miles you put in. Nothing really spectacular but you'd be welcomed onto my schools girl varsity team.
The side stitch is usually a problem for the beginner runner. When i first started running i was plagued by them the first couple months, but as i started running 3 and 4 miles a day for practice they went away. Once you run more they'll most likely become less and less of a problem. I've been running for a long time and i get them very rarely now.
If they don't then definitely look into your diet, maybe something your eating is causing it. But i wouldn't do that unless you've been running for quite some time and they still won't go away.
Try not to grip your side when u have a side stitch. Try not to slouch over either. Keep upright and breath in through your nose and out through your mouth. I know it can be very hard cause tbh i didn't follow that advice too much, but try practicing it. A side stitch probably won't go away if u keep running but trying that increases the chance it will.
Lastly I'm gonna guess you care about running cause u took your time to post about it. Make time to run. MAKE TIME TO RUN. You can become good at this sport if you just put the miles in. Generally the more miles the better. The top high school runners are putting in 60-80 miles a week or more. I'm not saying go out there and run that, but it just puts things into perspective.
I'd say getting up to 30 miles a week for a sophomore running their first season is respectable. Especially if you have a coach that doesn't endorse a high mileage program. Don't get caught up so much at your pace is, just focus on the miles for now. Don't go super slow, and make sure to have some hard days where you are pushing yourself, but don't be afraid of incorporating a lot of slow long runs. Ramp up slowly so you don't get injured. Look up the 10% running rule.
Good luck and I hope you have a good cross country season!!!! Hope I helped answer your question.