My Macbook Pro is saying i dont have enough space to update from Mojave to Catalina, but i have 20gb when it says i need 11gb. Any tips?

Steve is right. You do not want your hard drive to get too full. Now is a good time to install an external drive so you can transfer files on to it, then delete them from your hard drive to clear needed space. These days external drives are reasonably priced, very compact and easy to install with a provided USB cable. Most of them do not require external power. You may have to reformat it, though. This will easily solve your problem. Also, if you do not already have an external backup drive, I would get a second drive for that.

I believe that 11 GB is for the initial download or expanding it, but others have reported that more than 30 GB is actually needed. I would have at least 35 GB to be safe. When a Mac runs out of disk space, or is unable to page to disk, it could freeze or crash. If this happens while updating the operating system, you could end up with an unbootable Mac without a working operating system.