Worried

So I took a few HPTs at 4 weeks with super strong HCG lines, I've been mild cramping but no spotting so I thought everything was fine.. I randomly decided to take one this morning just to use them up, and I'm shocked to see the HCG line is more faint than it was last week.  Should I be worried?? Is there any way this does NOT indicate I'm gonna miscarry?  I have my sonogram appt scheduled for Monday- at 6w2d 😟