For a structural bulkhead of any kind I would use 2 at least, maybe 3. Fillet the corner first with thickened epoxy by using a piece of plastic or wood that has a round corner. This stops the biax from having to take a corner and leaves it in a gentle curve. You might find it easier to cut the biax into easy to manage strips about 2' long or so and wetting them out before putting them on. Do this on a piece of plywood covered with thick plastic wrapped over the edges and stapled or taped underneath. Wet the biax thoroughly but make sure there is no excess resin as it adds nothing. Use the roller to squeeze out any bubbles. Overlap the biax, first to one side and then the other and finish up with a layer down the middle. Or use several widths of biax, starting with the narrowest and then the thicker ones.
ps You have used the quote button more in this post than I have in over 2000 posts.