If you notice shadows on the photo you have scanned, the cause could be a bad room lighting. Used diffused light.
If you don't use the flash during the scan, make sure not to shade with the hands or with the device.
Remember that the best way to take pictures is to tilt the device of 45 degrees and use flash.

If the picture looks distorted, make sure you have used the correct aspect ratio. if the aspect ratio is not listed among those available you can manually measure (measure key).
If the aspect ratio is correct, then you can open the photo then tap on EDIT, then choose the button for the border picking. Now verify that the capture frame is correct otherwise edit them manually. Save the picture to apply.

To apply filters on photos, choose the photo to edit than tap it. Now tap on Edit, then choose the filter to apply. note that you must tap on DONE to save the photo.

You can share single photo or multiple photos.

Tap on EDIT on bottom right, select the photo or the photos you want to share (you can also tap on the SELECT button on the right of each label to select all the contained photos) then tap on the share button (bottom left). the standard iOS share window appears; select an option then share.

You can also choose to share an entire photo section, by tapping the SHARE button on the right of each collections.

Note that the FREE Memories apply a watermark on the photos. You can in-app purchase to avoid watermarks.

You can save single photo or multiple photos on your camera roll. This is a premium feature available as in-app purchase.

Tap on EDIT on bottom right, select the photo or the photos you want to save (you can also tap on the SELECT button on the right of each label to select all the contained photos) then tap on the share button (bottom left). The standard iOS share window appears; select the SAVE icon to save selected items in the standard camera roll.

Note that the FREE Memories apply a watermark on the photos. You can in-app purchase to avoid watermarks.

to measure the aspect ratio, tap on the camera button then tap on the "Aspect Ratio” button.

The menu will appears. Now tap on MEASURE. Place your photo on a white sheet of paper, then point the photo from above, taking the device parallel to the plane. Watch the Bubble level and move the device to turn the bubble to GREEN. Wait for the measure process, then capture the photo.

To restore to default a cropped or edited photo, tap on the photo to obtain the bottom bar menu. Now tap the border picking icon (5th from left) then tap on DONE. 

The original shot will be restored.