`watch -n 100 'sh script.sh >> /path/to/output/output.txt` doesn't write to output.txt?

I'm currently executing the following:

watch -n 100 'sh script.sh >> /path/to/output/output.txt' &

It's been running for 30 minutes (I can verify with ps -ef | grep watch), however there's nothing being written to /path/to/output/output.txt (the file doesn't exist). script.sh executes commands that prints to terminal, so shouldn't the >> be directing everything to output.txt?