You have two options....
You MAY be able to lock the car using the passenger door.
Unlock the other doors. Get out with the car running. Open the Passenger Door and press the lock button. This should lock all of the doors.
The only caveat with this one is that the key may not unlock the doors wirelessly. You may need to pop the cover off and unlock it manually using the lock cylinder.
Option two is to find out why the remote start wont work...
Is the check engine light on? If so, No Remote Start.
Is the fuel level in the Reserve (red) section of the fuel guage? If so, No Remote Start.
Is the Adblue light on? If so, No Remote Start.
If none of these scenarios exist, then maybe you are not pressing the buttons in sequence fast enough...
Lock, Start, Start. All within a few seconds.