Wow...I think you need to be the adult here and set him straight.
I would explain to him that managing Type 1 diabetes is not simple, and that "controlling" blood sugar levels is not as easy/simple as it sounds. It's not just about what you eat and how much insulin you take, but also about so many other factors that you have no control over (hormones, weather, potency of the insulin you're using, accuracy of the meter you're using, pump issues, stress, etc). If I start to get a little sick (something completely out of my control), my BG shoots up for days. I have very little control over this. If my infusion site goes bad or somehow gets dislodged, my BG will shoot up if I don't notice it right away. The week before my period is filled with huge swings (mostly highs) because of the hormonal surge you get before your period starts (which increases insulin resistance). And then I bottom out the day my period begins.
The bottom line is that being a full-time pancreas is really, really hard. Pumps make things a bit easier, and the faster-acting insulins are great, but a lot of care we have to give ourselves is imperfect. We still have to make tons of decisions each day that affect BG levels. And these decisions (which feel more like educated guesses) have deadly consequences if we get them wrong. For example, my BG was 163 when I woke up this morning. That's high. BUT, I was about to commute to work, something that usually results in my BG bottoming out. Do I ride that high and keep an eye on it, hoping it doesn't go higher? Or do I correct and risk my BG dropping while commuting, during which time I could pass out and fall onto the train tracks? Or wreck my car? Or inadvertently walk out into traffic and kill myself (something I almost did a couple of years ago when I went low)? These are tough decisions. People think that we just take insulin and eat the right foods and everything is magically ok, but it just isn't that simple.
And you may want to literally walk him through your day and explain all the decisions you have to make on an hourly basis. All the times you test. All the times you calculate exactly what you're eating. All the times you have to think about diabetes and make a really important decision.
Also (and you can print out my response and show it to him), controlling BGs when you're a teenager is virtually IMPOSSIBLE. The surge of hormones that you're randomly getting wreak havoc on control. An A1C of 6.7 is AMAZING at your age (mine was rarely under 8.5 when I was your age, and I had more double-digit A1Cs than I care to remember). You can't control your hormones. Trying to pin down basal rates at that age is hard because your body is changing on a weekly basis. For me, things got way easier once I hit my early 20s and my body calmed down. And, I personally think that achieving control is even harder for women, because we have the whole monthly cycle thing to deal with.
In addition...is your guidance counselor a doctor? If not, he has no authority and is in absolutely NO position to comment on your control.
I think the key is being calm and talking to him like an adult. Assuming he doesn't have T1, you know WAY more about managing T1 diabetes than he does. His point of reference may be someone with T2 diabetes, and it just isn't the same thing.
Finally, I don't think your control has to be perfect to be a counselor at a camp. There are so many teens going through the challenges of living with type 1 diabetes and few of them have "perfect" control. The important part is that you're doing all the things you should be doing - testing frequenting, using a pump, communicating with your doctor, etc. That's how you can be a role model to other kids.