I missed checking in one week and when I came back and checked in, it posted to the previous week instead of this one.  Now I'm a week behind.  Any way to fix the check in date? 

Go to your weight loss graph in the "my progress" section. There will be a link to edit an entry. Select this and you should be able to edit your weight for any check-in.

 You've missed the point.  I missed a check in for August 17 and checked in August 24 with my weight as 238.  It still has August 24th as my next check-in even though it should be August 31st.  I'm a day late and when I tried to put in my weight it changed my 8/24 weigh in rather than moving forward to 8/31.  Yes, I'm a day late but I was on the road and could not check in yesterday.  Not that it would have mattered since it isn't working...  How do I move this forward to the current week???

Also, I've never gotten the promised mid-week reminders...

Underneath your check-in date there should be a link to "edit goals". From here, change your check-in day to Wednesday. This will allow you to check-in tomorrow. Afterwards, you can change your check-in day back to the day you originally selected. This should also trigger your check-in reminder email.