The Wongers, in second, now sit six points behind the Lilywhites in the standings following the weekend’s disappointing 3-1 defeat at Lincoln Moorlands Railway.
But victory could see Horncastle close the gap and put additional pressure on the defending champions.
“It’s the big derby for us, and we don’t want to lose this one,” joint-manager Shinn told The News.
“They won on Saturday so they’ve got the advantage, but hopefully we’ll pick it up for this game.
“We can’t lose to them again.”
Skegness have already recorded league and cup victories at Horncastle’s expense this season, something which Shinn and his squad want to avenge when the two opponents meet at the Wong on Saturday (KO 3pm).
But the main aim is to reduce the gap on the side above them, who still have two games in hand.
And Shinn isn’t giving up on the title.
He said: “They do what they do well, but they’re not unbeatable.
“They make mistakes like everyone else and we’ve just got to try to make the most of that if they come our way.
“There are still teams a few points behind us who are still in it.
“We’ve got Nettleham the Saturday after and they’re doing well at the minute.
“It could be a defining few weeks coming up, not just for us but for the whole league.”
Luke Blondell netted Town’s consolation on Saturday.
It was the Wongers’ first fixture since December 17, and not the return Shinn and fellow manager Mickey Stones wanted.
“It was our first game after four weeks off but it wasn’t good enough,” Shinn added.
“Too many players were idle and they need to man-up.
“Maybe we were too kind and didn’t work them enough before the game, it’s partly our fault.
“But there wasn’t enough effort.”