how about give 1 medal bonus every 1 week full web attendance, and bonus 2 medal at end of the month for full attendance.
Example for full attendance :
you can get up to 6 medal per month
1 every week and bonus 2 medal for full attendance
if you miss 1 attendance, you'll not get 1 medal from 1 week, and also you'll not get 2 bonus medal at the end of the month
This is the example if you miss an attendance: