You need to practice seeing and adjusting color. This comes from experience and the more you match digital to film the better you will get. Exposure, white balance and tint all play off each other and effect each other. With these 3 variables you can match digital to film almost exactly. It may just take practice when you first begin.
You are trying to match to a film scan that is not the correct film stock or was not scanned on the correct scanner for the presets you are using. For example, if you are using the Portra 400 preset, you will not be able to successfully match a film scan from Fuji Superia 400.
You are trying to match a film scan that was very underexposed/overexposed. Underexposure is the worse of the two evils, with underexposure creating dramatic color shifts and muddy unrecoverable blacks.