text jumps unintentionally

Hi Everyone, I'm looking for help.

The problem is that I've put some text (few words) beneath a 5 sec photo in Imovie, and The text jumps unintentionally.

example:

First 3 seconds: Hello guys, thanks

in advance

Second 2 seconds: Hello Guys, thanks in

advance

Does anyone know how to solve this problem and freeze the textbar?

Thanks in advance!