help creating quality vector image

Hi, I am a complete novice.  I have Corel 12 and have been asked to create a logo for a friend to use by a printer to have put on a banner.  I started with shapes and made up the logo and saved it as a CDR file.  I sent the file and got word back that the quality of it was not high enough and the file needs to beat least 5mb in size. Is there something I should have been doing that I didn't do please?