USVI-On-Line

I am flying out of STT on a monday but see no return ferry from Virgin Gorda. Any suggestions?

"Yes", there are few and far between straight shots from STT to VG and back. In past years, we have gone straight to VG, then second leg of trip headed on to St. John.
To my knowledge, your only real option is to do what we did.
Travel from VG to Tortola. Then get a ferry to St. Thomas (in our case, we went to St. John).
We took Speedy Ferry out of VG. (We had been told that they are more reliable than Smith's.) That was a few years ago. Anyway, we then landed in Road Town, Tortola. Most, if not all, of the ferries to St. Thomas and St. John depart out of West End, Tortola. (There are a few out of Road Town, but, very limited hours of those one.) So, most likely, the process will be to get off of the ferry boat in Road Town, collect your luggage, then take a cab to West End. (about a 25 minutes ride). Really lovely ride along the coast for a bit. At West End, you will need to pay a departure tax and of course buy ferry ticket. I think we took Native Son, but, there are multiple outfits down there and you can just grab whichever one suits your timeline. Prices are all pretty much the same. Not sure about the customs thing. But, when we went, we had to clear customs in St. John. So, I would "assume" that you would need to clear customs in St. Thomas.
The process is a little but of a pain. But, good news is that the ferries between VG and Tortola run often - as do the trips from Tortola to St. Thomas and St. John. Definitely worth the headache.
We haven't stayed on Virgin Gorda for a couple of years. But, it is a truly unique and special place.
Have fun!