expect 1 Master 2 Slaves with sentinel instead 3 Masters

I used this configuration below to create a cluster with 1 master 2 slave with 3 sentinels, but it keeps creating 3 master with no slave attached, what did I do wrong here,
```
version: '2'
services:
redis-cluster:
environment:
IP: '0.0.0.0'
SENTINEL: 'true'
MASTERS: 1
SLAVES_PER_MASTER: 2
build:
context: .
args:
redis_version: '5.0.5'
hostname: server
ports:
- '7000-7050:7000-7050'
- '5000-5010:5000-5010'
```