Should I be worried about this?

I got my first BFP at 12 dpo (Sunday night after a 4.5 hour hold), took another FRER Monday morning (13 dpo) and one this morning (15 dpo)

I feel like my tests aren't getting dark enough. The line showed up faster today, but it doesn't seem much darker.

Its the first time I've ever had a BFP, so I just don't know what is "normal". But I'm going for betas after school.