I need help with my level! (sorry for my english)

So, I´m creating a level and when I start playing the character goes like flying, It is a normal level with normal floors etc.

So I put the nav mesh bounds volume and I watch that, Ihave no idea what is going on, as you can see, some kind of hill just appeared with no reason, I´m new in this program so I don´t know what the hell is causing this, I aprreciate any help.