There's not really such a thing as lines not being dark enough.
Every woman has a different base level of hcg in their system (usually between 1 and 5 but can be less than 1), and implantation can happen from 6dpo to 12dpo (8,9 and 10dpo being the most common), so hcg levels vary greatly from woman to woman, and from pregnancy to pregnancy.
As long as your hcg is rising as it should be, there's no indication of a problem. Your lines are getting darker, so that indicates your hcg is rising.
Clearblue weeks indicator needs 20,000 miu to get the 3+ result. It can take a bit longer for some to reach this than others, it's not exact. It's 200miu for the 2-3, so your levels are somewhere between 200 and 20,000.
I only got a 1-2 at 16dpo and faint lines until like 20dpo, but they got darker so I wasn't worried.
Only 6+6 currently, so not out of the woods yet, but definitely far along enough to say my line strength meant nothing (as I'm past the point of a chemical now) and the pregnancy symptoms and morning sickness are in full swing now, so my hcg is obviously at a healthy level!
Your tests might stall at a certain point, especially on strip tests. Each one will have a slightly different amount of dye in, and at 5 weeks, it's better to stop testing now as you're reaching the hcg levels that will prevent further line progression (some tests only get so dark).
Unless you have bleeding and/or one sided pain, try not to worry.