How do I do this???

Have my very first half mary on Sunday. Will be running with my Garmin and I know what pace I can sustain for this distance based on my training runs. My question is how should I pace myself?? Do you just try and maintain the same pace for the whole race or is there more to it than that?? I am a sloooow runner, and figure it will take me 2:15 to complete.

All advice is welcomed and appreciated. Thanks!