Am I likely to need other braces when I’ve finished the invisalign treatment?

Q. I was told that there could be a chance I\’d need fixed braces at the end of my treatment because of two stubborn teeth (next to my very front teeth) the whole point of me getting invisalign was so my teeth could be fixed completely and my orthodontist said it was likely that it would fix my teeth but then sends me a letter after i\’ve already paid saying I may need fixed braces! Is this right?? Is he just trying to get more money out of me?,