I had same thing. First test was so faint hubby couldn't even see the second line. Got progressively darker over following weeks. I would have been probably only 1 to 2 weeks pregnant at that point. I'm now 20 weeks.
I had a mmc early in the year. I was in same position as far as not wanting to get too excited as there's still possibility it's an evaporation line, or a pregnancy that doesn't take eventually. Honestly, I feel for you, it's so hard being unsure. I'd suggest getting your bloods done again and hold off as long as you can for the scan. First one I had made it hard cos at only 4 weeks they saw sack but couldn't confirm an actual bubba that early!
Also do bear in mind that if you had mc very recently you may still get a second line. God bless you and hopefully your bubba! X