More HCG the darker the line?

Today is 26 days past our iui.

I took my first test on 2/10, 15 days after and it looks like every test the line is getting darker. I’m assuming the darker the line the more HCG?

My doctor tested my levels last week and they were positive and recommended we come in 2 weeks for the first ultrasound. This is still a week away so just trying to ease my mind as I’m not sure what my actual HCG levels are now.

Any experience or advise would be super appreciated!