The national team boss saw plenty of room for improvement following Spain's friendly victory on Wednesday, but Santi Cazorla felt the result was not the most important thing
Goals from Santi Cazorla and Cesc Fabregas in the closing stages of the first half were enough to see off their opponents, but the coach was not impressed with his side's finishing at the Juan Ramon Loubriel.
"We had plenty of opportunities to score more goals, but lacked accuracy in front of the goal," Del Bosque told reporters.
"We did what we had to do as we won the game, but we should have done more. We were not assertive enough in my opinion."
Meanwhile, goalscorer Cazorla stressed that the most important thing for Spain is to improve rather than record big wins in friendy matches.
"The thing that really matters is that we make progress as a team," the Arsenal new boy noted.
"It was not easy on this heavy pitch and with the humidity, but I hope that everybody enjoyed the game."
Spain's next match is the World Cup qualifier away to Georgia on September 10.