How do I remove this?

Not sure what I have done here but I need to remove it as it is preventing me from rendering past 2 minutes and 58 seconds.

Its a grey line that appears to be stopping the render at that point

Any help would be appreacited!

Go to Mark->Clear in and Out.
or
Shortcut, option+x if you are on mac, not sure for windows, (alt+x)?

For anybody new to Resolve Editing, be sure to go through the free textbook & training videos:

"The Editor's Guide to DaVinci Resolve 18"

available on Blackmagic's Training website:

https://www.blackmagicdesign.com/produc ... e/training

You'll find these are enormously helpful, even if you have experience with other editing & color platforms. There's tons of shortcuts covered, which will help cut precious minutes off every session. The 4060-page manual is good as well, but the textbooks present it in a much more concise way. (Coming soon is a Resolve 20 training update.)