If I fast for 5 days will it ruin my metabolism?.?

So I'm 5'2 (teenager) and I weigh between 115-117 pounds and I want to go on a fast just to get all the junk out of my system because lately I've been bad and have been eating some sweets and I'd just like to eat healthy again. The reason I say 5 days is because I'm getting braces in 2 days and... show more So I'm 5'2 (teenager) and I weigh between 115-117 pounds and I want to go on a fast just to get all the junk out of my system because lately I've been bad and have been eating some sweets and I'd just like to eat healthy again. The reason I say 5 days is because I'm getting braces in 2 days and my orthodontist said that my mouth might hurt too much to eat but mostly I'm aiming for 5 days.
Although I've never fasted before and so I want to know if it'll mess up my metabolism?
As well I know I'll probably lose some water weight and gain it back but will I gain MORE weight then I started with? Again I'm not doing this to lose weight but I want to know if I'll gain more because I'm happy at the current weight I'm at and I'll be pretty bummed if I gain more weight.
If you answer thank you!
Update: I just read it I meant I'm aiming for 3 days
Update 2: Again as I said I am NOT looking to lose weight I am perfectly happy with the weight I'm at if I had to be at a lower weight 110 would be my lowest I don't want to gain nor do I want to lose weight.
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