New to this - question

Hi, I'm just wondering if anyone knows the answer to my question. If I took my HCG shot  11 days ago, and took a p-test this morning. There was still a faint line showing. I'm supposed to go for my bets on Friday. 
I'm confused how I'll be able to get a positive pregnancy test by Friday if the shot is still registering in my system!?? 
Anyone have some positive stories along the same lines!?? Just looking for some hope here. 

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