Anyone that knows how to take blood pressure?

I was in L&D and the nurse had the cuff on me so loose that I could fit my whole other hand in it with my arm, all the way past my wrist. After getting high BP all day at home, I was getting low (normal outside of pregnancy) readings in L&D (119/78). I said that the cuff was too loose and that I don't think that's an accurate BP since I had been getting BPs in the 150s-160s/90s-110s all day, and she told me I must have my cuff too tight at home. When I put my cuff on, I make sure my fingers fit under it, which is the way I was taught when I originally learned, and the way the doctor taught me again since she wanted me to monitor at home. I told her this and then she said I must be in the wrong position, but I'm positioned the way my doctor told me to be, sitting with my feet flat on the floor and my arm propped up to chest level. Am I taking my BP wrong?

Also, when I was in L&D on Saturday I had BPs in the 140s-190s/90s-100s. At the clinic for my appointments my BP is usually in the 150s/90s-100s. Also, they usually take it with me sitting like I do at home, but she was having me lay on my left side (not that position should affect blood pressure to that extent)...

Sorry for the long post, but I'm honestly getting frustrated and sick of being treated like I'm doing everything wrong when I'm doing it the way I was taught.