"Is it true that you can be denied if you make mistakes during the interview at the U.S. Embassy in Manila?"
Everything comes down to the discretion of the consular officer conducting the interview and asking the questions. If you're filing for a fiance visa, they're really looking to see that you truly intend to marry within 90 days after you're in the United States. If you're filing for a spousal visa, they are looking to see that you have a bona fide, legitimate relationship. Some examples of that are if you've commingled finances, you've had a long term relationship, you've been communicating, or visited several times. But usually, you're not going to get denied for just making a simple mistake in the interview.
A lot of times, if you realize you made a mistake, you can come back and correct that and you can ask the consular officer to repeat the question if you don't understand it. Listen carefully and intently. Make sure that you understand what they're asking and if you don't, simply ask them to repeat the question. Sometimes the consular officers will try and push you into answering questions rather quickly because they do have to interview quite a few applicants and a lot of times they're actually trying to trip you up a little bit. But that's okay, just relax at the interview. Slow down and if you don't understand the question, ask again. Generally, the worst case scenario is they may submit what is called an RFE, a Request For Evidence.
