Pregnancy test question.

I found out I'm pregnant a week or so ago and have bought a stockpile of the .88 Walmart test to test every few days to make sure my line is getting darker.
It's getting darker but I don't know how dark the test line will get on them. 
Will it pull color from the control line like a First response will?  
Yesterday's 
 March 16.  ( day after I tested postitve with a first response) 
March 18
 I just don't know how much darker the test line can go to. 
Thanks for your help 

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