Celtic have a game in hand against Kilmarnock at Rugby Park, and have the opportunity to close the gap further in the two remaining games against Rangers, who have taken four points from the first two clashes between the teams this season despite being outplayed in both games.
McGinn said six points from the matches against the champions has to be the target now.
"The players were on a downer after the Hibs game, it was a killer goal to lose at the end," the Northern Ireland international said.
"Our confidence was high after the win over St Johnstone last weekend and we played really well against Hibs for the first 20-25 minutes.
"We had chances to tie the game up and I had the chance myself that I should have scored.
"It was a great knock down from Georgios but it was a good save from their keeper.
"So it was so disappointing to lose the late goal.
"We have to keep plugging away and hopefully the gap doesn't get much better.
"But we have a game in hand and still two games to play against Rangers. "And realistically, the only way we can close the gap is if we win our game in hand and those two games against Rangers.
"Thankfully, we get the chance to put things right against Hamilton on Saturday."
Galbraith is hoping his last-gasp winner at Parkhead signalled the end of his injury nightmare and the start of his Hibs career.
The 19-year-old has had to fight back to fitness after undergoing operations to cure ankle, knee and groin problems while a youth team player at Manchester United.
Galbraith, who moved south from Hearts as a 16-year-old, returned to Edinburgh last summer to kick-start his career with Hibs.
And after coming on as a second-half substitute for Colin Nish, he scored his first goal for the club in injury time to take the Leith side to within two points of their opponents in third in the SPL table.
The teenager admits there were times when he thought he would never recover from his injury traumas.
"There were times I thought that," he said.
"I saw more doctors and specialists when I was at Manchester than anything else.
"I had the ankle operation and the knee operation only to find out I needed more surgery for another injury.
"I never kicked a ball for 10 months, that was when I started to get really down.
"I was only 16 or 17 when it started and I was away from home and you do wonder is it meant to be.
"I think things happen for a reason and at least at Manchester United I was in the right place to get the right treatment and see the right people so that I was able to get a second chance.
"With the three injuries I had anything could have happened but I was well-looked after, the club were brilliant with me and I cost them money seeing specialists, flying here there and everywhere to see people.
"I had good people around me, family and the doctors in Manchester tried to keep my spirits high and through hard work and good medical care I managed to get back playing.
"I have worked hard, everyone will say that, I have kept my head up and it's more a relief when I scored against Celtic.
"It made me feel as if i was all worth it.
"Hopefully there is a few more to come.
"I don't want to live in the past."
Coming to Hibs I knew it was a great opportunity for me.
"Hopefully I am over it now and it's all about staying fit and doing well for Hibs."