You've already taken an important step to safe anchoring under sail: you have a Bruce
anchor on an all-chain
rode.
The Bruce sets well in almost any bottom. While its ultimate holding power isn't likely as high as some other
anchors -- according to several anchoring test results and anecdotal information -- it sets easier than just about any other
anchor. That's worth something!
I think I'd leave the main up awhile after anchoring. It there's any wind, this will create at least some load...perhaps enough to give you some confidence that the
anchor is set -- or is likely to set deep when the wind pipes up.
And, until you're sure the
anchor is really set, keep a watch onboard.
Bill