Question about mg in edibles

I'm super sensitive to THC. I only smoke CBD flower with like 0.9% THC and after one joint I feel something like a little high and that's great for me. I want to try doing edible with this hemp flowers. Basing my calculation ONLY on THC %, I see online this formula to calculate mg of THC --> (%THC/100) * "mg of weed you want to use" = mg of THC in the receipe.

This is my plan:

10 g of 0.9% THC; 9 brownies. Applying the formula --> (0.9/100)*10000 = 90 mg of THC in total. So if the THC is evenly distributed, I will get that a single brownie contain 10 mg THC. Right? So my plan is to take 1/2 brownie (5 mg of THC) and wait 2 hours.

I'm really scared because I know that with edible there is not "stop" or "coming back"... This is a good plan?