Updating Sheets

I bought some sheet sets back in December thinking I would sew them together to make new Duvet covers for Ruth and Lily's bed--maybe as part of their Christmas. Well, almost 5 months later the Queen of Unfinished Projects has finally signed this one off: two new sets of Duvet covers made from the themed sheets each girl picked out (Ruth picked Dora and Lily picked Disney Princesses). It sounded simple--sew two sheets together like giant pillow cases. Bleah. I don't think I'm going to do this one again. Not easy. Unless I can get some sewing help on how to finish off seams properly and how to measure and cut such large projects. At leas the girls will stop asking me when they are getting their new sheets--Lol!