Like any learning experience, there is always doubt in how efficiently you have learned. Although, I wouldn't say it was all that useless. There are levels in Nihongo and a difference in how we were taught compared to the casual conversation type of communication. Just try and learn what you can while still in Cebu yet don't expect that what you have learned is enough. Even the Japanese themselves have a hard time mastering their own language.
The best way to learn conversational Nihongo, is still of course, immersing ourselves with the Japanese and talking to them.