Line progression help from 9DPO to 13 DPO

Today is around 13 DPO. This is my line progression from 9DPO (first positive) to this morning, all taken with FMU. I am concerned about today's test. I had a chemical pregnancy in June, then a MMC at 7 weeks in October so I am very anxious about another miscarriage or chemical. My tests were getting much darker every day through yesterday (12 DPO), but today's test looks the same as yesterday's. Should I be worried? I also want to note that today's test was from a new box of FRER. The previous three days were from a different box (but all the same box). Could there be variation between boxes? Anxiety through the roof today ugh. Thanks for any guidance and support!