Take a look to WiFiManager and things around it.
It creates an AP by design on startup if there is no connectivity to your saved once WiFi SSID.
Once you have your router SSID / pass saved through the auto connecting temporary AP in question, the it should not appear anymore.
Alternatively, you can clean the code completely from WiFiMAnager and use the hard coded credentials to your SSID.
If this is not the problem you faced, then you may search for EraseFlash.ino, then use it to make sure you clean any previous firmware left-overs.