According to the documentation, this is what you get if the network currently has enough space and is rejecting new nodes, so all is good on your end.
This from @wydileie is currently the best available join command, attempting to join as a node every x seconds until it works:
until grep -q "Handling NodeDuty" ~/.safe/node/local-node/sn_node.log; do safe node join; sleep 30; done