If your scans are going into 'Pictures' they're probably jpeg images (rather than pdf documents).
Before trying anything at all complicated, the good old trusted solution of 'turn it off and turn it on again' may well work here. i.e. if you turn off BOTH your computer and your printer and then turn them both back on again, you may well find that the default scan setting (that worked for the first three pages) have been restored.
If that doesn't work you'll probably need to open an image-processing program and use the 'Acquire' (or similar) option within that. (I'd never use an on-screen button for scanning anyway, since it gives you no control over the area scanned or the resolution used. It's always better to open an image-processor first).
However the problem I've got is that it's not clear, from the Epson website, which (if any) image-processor is included with your printer's software. If you can find something suitable (or if you've got something like Photoshop or GIMP anyway) you'll need to go to the 'File' menu and look for an option to 'Acquire' (or perhaps 'Import') a scan.
If you've got no suitable software, download and install Irfanview (which deserves a place on everyone's computer anyway - it's a much better image viewer than the rubbish which comes with Windows). Then open Irfanview and go to File>Select TWAIN source to check that your printer is shown there. Next go to File>Acquire/Batch Scanning to open the driver that allows you to control your scan settings. Once you've scanned the image into Irfanview, go to File>Save As to save the image to your Pictures folder.
http://www.irfanview.com/