How many times should I test my blood sugar in one sitting?

Hello,

I am pre-diabetic and I purchased a blood glucose meter. Now, such as this morning, I have found the meter to be wild in its results. I have been using it for a few days and have heard it can be +/- 20%. So I decided to test with a couple of strips to see the results. For this morning my results for fasting were: 102, 87, 80, 92.

I averaged them out and it came out to 87.75.

Is this what I should be doing? I am very new to all of this and I couldn't find an answer online.

Thanks for any advice!