Apricot tree branch die back

I have a new fan trained apricot that went in over winter. It blossomed nicely and has now come in to leaf, but today I noticed that one of the branches has died back from its tip, which had previously been in leaf. I have cut the affected tip off, several inches below the dead area (within an area that still looks healthy). I don't have any pruning sealer to hand but may get some and cut again a little further back if people think that is appropriate (recommended brand of sealer?). There are a few very small beads of resin along the dead and dying length of branch. My concern is that this might be bacterial canker. Does this sound probably? I initially cut the tips of each of the existing branches when the tree was first planted over winter. This was at the recommendation of the seller, even though it is at odds to the usual advice - he said "this time only" for the winter prune.
Please advise!
thanks.