How/where to look behind me while driving to get over to other lane?

im 16 with my permit and new to driving and I'm having a lot of trouble seeing when i merge to the lane in the left of me. My mom yells at me because i slow down a little and try to see and she tells me "quick looks" but I can't really see when I turn my head. I drive a honda civic. Idk if am too short (im almost 5'2'') but I don't think thats it. Should I look out the back window or side window in the backseat? I try to use my mirrors as well but I just have difficulty knowing if I should go or not, please help me thank you. I don't want to never be able to drive

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