Time the tides and currents (they may be different - current change may lag the tidal change by a couple of hours - check your local guides). Our first "offshore" trip was out the Port O'Conner jetties from Texas
into the Gulf of Mexico
(in our Morgan
41 with 62 HP inboard), 2 longish tacks in gentle seas for less than 2 hours, and then back in. It was the back in that crushed us - the current was flowing out, against a moderate onshore breeze, and the standing waves in the extremely narrow channel between jetties was more than nervewracking, plus an outgoing ship to pass on the way in - I nearly had a breakdown (literally - I was in tears) once we got in safely. Wife and kids
on board, and no experience at all. I know the St. John's is wider (although we've sailed past it offshore
2 or 3 times, we've never gone in or out), but still - time the tides/currents carefully, and if opposing any breeze, factor in the possibility of larger seas (even if the current is with you).
Good luck, and have fun. Our second time offshore
was a dream, and many more since then.