Robin van Persie scored the only goal of the match in the fifth minute on the day Van Gaal confirmed his 23-man squad for the 2014 FIFA World Cup.
But the national coach expressed his disappointment at his side's failure to build on that early lead, despite numerous opportunities to find the net.
"We are too careless with the ball," he is quoted as telling SBS 6. "In the first half, there were many opportunities for us to create opportunities, but we have not taken advantage of them.
"We have made a brilliant goal, but it should have been 3-0. We had two fantastic attacks."
Van Gaal looks set to employ a five-man defence in Brazil, and praised his backline for limiting Ghana's attacking threat.
"In the second half we created nothing, but gave absolutely nothing away," he added. "That goes for both the first and the second half. This is the advantage of this system."
The Netherlands meet Wales in Amsterdam on Wednesday in their final pre-World Cup warm-up.
