How do I correctly add worker nodes to my cluster?

I am trying to create a cluster with the following parameters on Google Cloud:

1. 1 Master
2. 7 Worker nodes
3. Each of them with 1 vCPU
4. The master node should get full SSD capacity and the worker nodes should get equal shares of standard disk capacity.

This is my code:

#Create the cluster
CLUSTER = '{}-cluster'.format(PROJECT)
!gcloud dataproc clusters create $CLUSTER \
    --image-version 1.5-ubuntu18 --single-node \
    --master-machine-type n1-standard-1 \
    --master-boot-disk-type pd-ssd --master-boot-disk-size 100 \
    --num-workers 7 \
    --worker-machine-type n1-standard-1 \
    --worker-boot-disk-type pd-standard --worker-boot-disk-size 200 \
    --max-idle 3600s \

This is my error:

RROR: (gcloud.dataproc.clusters.create) argument --single-node: At most one of --single-node | --num-secondary-workers --num-workers --secondary-worker-type can be specified.

Updated attempt:

#Create the cluster
CLUSTER = '{}-cluster'.format(PROJECT)
!gcloud dataproc clusters create $CLUSTER \
    --image-version 1.5-ubuntu18 \
    --master-machine-type n1-standard-1 \
    --master-boot-disk-type pd-ssd --master-boot-disk-size 100 \
    --num-secondary-workers = 7 \
    --secondary-worker-type=non-preemptible \
    --secondary-worker-boot-disk-type pd-standard \
    --secondary-worker-boot-disk-size=200 \
    --max-idle 3600s \
    --initialization-actions=gs://goog-dataproc-initialization-actions-$REGION/python/pip-install.sh \
    --metadata=PIP_PACKAGES=tensorflow==2.4.0

I don't follow what I am doing wrong here. Can anyone advise?