You can increase the default WebDrive Storage Quota Limit for your site profile by making a change in the registry. If the drive is showing less available space than your drive should have, please make this change: 

Open the registry editor and go to HKEY_CURRENT_USER\Software\South River Technologies\WebDrive\Connections\(Your Site Profile Name) and then find the entry for QuotaMB and change the value to something greater depending on how large you would like the limit to be

Here is a PDF guide for this issue as well: