By default, the .ova builds a VM with 3 network interfaces. it sounds like you just want to build a 1-interface vSZ.
If you want to build a SZ with a single IP, then follow these steps:
1. Power-off the VM
2. Go to the VM settings, delete virtual NICs 2 & 3
3. Power-up the VM.
Continue with the set-up steps again.