Sensor Error 1?

So my 12th sensor is on its third week. I restarted it this morning. It was starting up fine, I went and took a bath and when I got out it had ??? showing. I took it with me to work, kind of ignored it, took a look at some point it was asking for blood. So I put in a reading- 87. It said ERROR 1. I put in another reading- 95- because I didn't know what else to do. It continued saying ERROR 1 and showing pictures of a sensor being inserted.
After about an hour and a half of that, I hit Stop Sensor and then Start Sensor and in two hours it let me start up with no problem.
Having come home and looked at what a Sensor 1 error is, I'm still confused. This is suppose to happen when the blood sugar is way off of what the Dexcom figures from the previous calibration- but this was the first calibration!

I just calibrated it again (about 8 hours since it started giving readings again) and the meter said 144 vs the Dexcom 178, which is significantly off but not all that bad- did not provoke any error readings at least. I think the test strips I'm using right now aren't so great and maybe I should use a different batch to see if I get better consistency.

And I have another (small) Dexcom problem, which is that I was planning on site rotation, arm to abdomen to arm. Sensor 10 went on my arm. My plan was that sensor 11 would go on the abdomen, and I'd stop using it a week or so before my GI visit, and then sensor 12 would go on my arm and be there during the GI visit.
But sensor 11 on the abdomen stayed only a night, and sensor 12 on my arm will be on its 22nd day if I wear it to the GI visit. So the question is, do I put sensor 13 in an arm and screw site rotation? Do I put sensor 13 in my abdomen and hope that doesn't bother the GI doc too much? Do I try and stretch sensor 12 past 21 days? Do I wear sensor 12 as long as it goes and then go without a sensor until after the GI consult? Do I try a sensor somewhere else, like my butt or my calves?

I'm hoping for insurance coverage to make the matter of sensor stretching less important (need to call people tomorrow about that). But that may or may not happen.
I'm hoping this sensor is going to last but I want to pull it out as soon as it becomes uncomfortable and to not worry about doing things that might make the adhesive come off.
I want to do site rotation- I'm concerned about the red bumpiness of my arms. But I'm worried about an abdomen site anyways because my abdomen is not very pinchable at the moment.
I want to reserve my butt for Lantus and my calves for injections in public places. But in the grand scheme of things, I'm not sure that either of those things is important.