One last thing - IF you have to stop short, if you cannot complete your required number of edges in that one spot, it's okay. I'm not unreasonable.
However, in the next place you edge, you have to finish the edges you did not complete the first time.
AND you have to double your new number (I'm not unreasonable, but I'm not a softy, either!).
So if you get a 30 the first time, and you can only do 20 edges, then in the second location, you have to do those remaining 10 edges.
Then get your new number.
And double that number.
You better hope you don't get a 60 for that second number!!!