There is no resize option in the tool. You can pixelate and export. On export is resized based on your Pixelate settings.
If maybe there is too much difference you can always do a screenshot. Due all effects is based on shaders, user resolution and GPU may differ how they are processed. Afaik, there is not a big problem, but yeah all depends on what you're doing. Also i recommend use the tool in fullscreen, due windowed/fullscreen the shader can alter some details, so full screen for best compatibility-close to the export.