I'm not completely clear on what would keep you from doing the ride?
Is it sheer pain from cramps that have you doubled over? Is it the sheer volume of flow? Edited To Add: Or is it that you have been bleeding for 2 weeks, thus weakened, etc?
I have done 60-80 mile rides with a heavy period, although of course have no way to compare your symptoms/tolerance levels to mine?
Maybe describe exactly what part makes you unsure you can do the ride?
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury