I did an end pour today. All did not go well.

I raised the opposite end of the canoe, I made a damn of cardboard, covered it with plastic, taped it all around using duct tape. Mixed the epoxy and added wood flour. After pouring the mix into the end area the tape did not hold,

the mix flowed out at the bottom and along the lower portion of the sides

. I was unable to contain it so I scraped it out before it had fully cured. It had a consistency about like Styrofoam. I expected it to be as hard as the seam fillets.
Once I had the mess cleaned up,

I stood the canoe on end, not quite vertical and filled the end seam without damning it. This worked pretty well except that as the epoxy cured the deeper portion doubled in size creating a rather large lump that I will have to take down with a rasp or small grinder

.

What did I do wrong and how can I avoid this when I do the other end of the canoe?
"to soon old to late smart"