A lot has been said, and written, about breaking in a new pipe. Now, there are differences of opinion, but a good many of the members here will tell you to just fill the pipe and smoke it slowly. About the only concession I make to a new briar (years ago, I did the 1/4 bowl, 1/3 bowl stuff) is to be sure that I will be able to smoke the whole bowl in a reasonable amount of time. You can let the pipe go out and relight later -- not a week later, but it doesn't all have to be in one sitting. But, go slowly. It is never a good idea to overheat your pipe, but this is especially true with a new pipe that doesn't have a layer of cake to protect it.
Cake happens. It is a natural part of the combustion process. Actually, I'd recommend "reaming" the bowl with a wadded up paper towel after each smoke. That will help remove loose stuff and help keep the cake layer a bit more even.
It is hard to get cake in the heel with some pipes. A few of my pipes burn to the bottom with little effort. A few always leave some dottle. For those, no worries. If you are not ever burning the last bit of tobacco, there is not much need for a protective layer of cake in the heel.
So, don't fret about it. I think they've already given out this year's award for best-cake-in-the-heel, so you've missed out on that. Instead, fill up, fire up, and chill out. It's not supposed to be a chore. If you smoke it, cake will come.