I can't lie, I never really try, and I don't do it very often

But today I am ashamed to say I did, not very well, so it didn't help me one bit.
I got up and put on the small heater that my Granparents had not been using, for a couple of minutes, so as to stand infront of it and warm up, to then, once resonably warmed up, to turn it off. Since late Jan early Feb I have been doing this every other day or not at all, when away, or  late getting up.
However today, Auntie Beth heard that it was on, she told me that I didn't need the heater as my room is the only room in the house that has a built in heater. Plus the electricity bill has gone up and Pampa couldn't work out why. Once again I tried to tell her that the heater in my room plus Toby's house does not warm my room up, or throw out much heat. She did not believe me, in desperation I said well you've got the boiler so you should be warm enough. An angry silence followed that.
A few minutes later, she asked how long I have, had it, scared that I was going to get told off, I panicked and I very immaturely said "a couple of weeks" She could tell I was lying, like I said when I lie it is written all over my face. I tried to redeem myself and tell her the truth but by that point she was furious. Not in the shouting way, nothing like Granny, but in a calm way, she was furious that I had done something that even I hate. I lied. She asked my why I lied, I said because I didn't want to be told off, or be in trouble. I was sounding very much like a small child at this point, nothing like a near adult young woman.
She then said "You never lie to me, you can lie to her to get out of trouble" (Granny) "But never to me"
Then Granny walked in.
I said a very immature "Sorry" and walked out of the room. I then took the heater out of my room and put it in the spare room.
She said goodbye to me before she went to work, which shows she won't hold a grudge or dob me in.
I spent the entire day at Flicka dwelling on how immature and naive I was.
I thought I was mature for my age, compared even, to my father, but when something like this happens it shows I still have a lot of growing up to do.
I had been practicing my "Sorry Speech" all day in my head and to Seb, to his amusement, to now find out that Auntie Beth is not coming home for tea tonight, meaning she will be late back. Great. Not.

Up side, told Dad, he said that the heater wouldn't have made that much of an impact on the Electricity Bill, if I had been using it only a couple minutes a day, and that it was probably him for he has one and he's been using it to warm up his house.

Even so, I will still have to face my Auntie tomorrow, and hope she will forgive me.