I'm looking to do a 20x24 canvas and need 1980x2340 pixels. The photo I want to use is only 1880x2340. I would like to zoom on it. I am only 100 pixels short, is that going to make a difference? or do you think I will be ok?
The difference is very little. You can resize it if you are given the requirement to send a file with a precise dimension but otherwise send it as-is. This is because the printer must do a resampling of its own and if you do one before, there will be slightly more artifacts.
Most crucially for you is that you will need to crop since the aspect-ratio of your image and the canvas do not match, otherwise your image will get distorted. This is only a 5% difference which may not be noticeable depending on the subject. Other possibility is that the printer will do a proportional resize and then crop which may cause you to lose an important edge, so it is immensely better that you decide at the exact content and proportion of your image.
Usually, resolution requirements are not absolute. You are limited by the medium but viewing distance determines what resolution is perceptible, so between 200dpi and say 190dpi, most viewers would be unable to see the difference.