One option that came to my mind is save it using the Slice Tool:
1. With the Slice Tool selected, click on the "Slices from Guides" button at the top.
2. File → Save for Web
3. Select the "Slice Select Tool" (or press C) and select the slice you want to save (if you want to save multiple slides, select the additional ones while holding Shift down).
4. Select the quality of the image etc.
5. Save to your location of choice. Make sure to chose "Selected Slices" from the drop-down menu at the bottom of your saving window. (Just a note: it will create a folder with that one image, so just move it where needed and get rid of the folder after.)
Here's a video / GIF going through the process I've described above.
This way you don't have to worry about your section following the guides, because the tool will make sure to snap the slices to your guides.