The phrase "a hard time forgetting" is correct and usable in written English.
It can be used when expressing difficulty in letting go of a memory or experience.
Example: "After the breakup, I had a hard time forgetting all the good moments we shared."
Alternatives: "struggling to forget" or "finding it difficult to forget".
I will have a hard time forgetting about it now.
But more than the pain from his injuries, he will have a hard time forgetting the viciousness of the attacker's screaming curse as he cut Mr. Chandra's neck.
He has an intellectual appreciation of the anxieties of a champion, but he has a hard time forgetting how strong he is; while he remembers that, he can't worry as much as he knows a champion should.
Perry will have a hard time forgetting today's round, which included an 18-inch putt he missed at No. 13 that could have given him a two-stroke lead.
Robbins (69), Lunke (75) and Stanford (74) all finished at one-under-par 283 for the tournament, a stroke ahead of Sorenstam (73), who will have a hard time forgetting her wayward 4-wood on the par-5, 502-yard No. 18.
And remember that Adidas commercial – although something tells me you'll have a hard time forgetting it.
And since we're Americans, we'll have soon moved on from the decade in Afghanistan just as we're well on our way to forgetting about the nine years in Iraq — except for the Americans who fought, who have a harder time forgetting.
Though no one seems to miss the former site of Kooyong at ever-more modern Melbourne Park and no one seems to miss cozy Forest Hills in the great paved spaces of Flushing Meadows, my hunch is that players and fans would have had a much harder time forgetting Paris.
Marty Turco and Ron Tugnutt are going to have a hard time making Stars fans forget Ed Belfour in net.
As Walter, Mr. Combs will have a hard time persuading the audience to forget who he is; no matter how the scene is staged, he is likely to generate a laugh when, in the middle of a money-hungry fever dream, he says, "Rich people don't have to be flashy".
It also does the job of personalising the reality of slavery, the nature and legacy of which many people can have a hard time understanding – and would sometimes rather forget.
