Pillager raids always end after the third wave

I’ve been killing pillager captains and then going to villages for the raid to start, but the raids always end after the 3rd wave and I have no way to get totems of undying, what can I do to fix this? (Minecraft bedrock windows 10)

The difficulty of your game influences how many waves a pillager raid would have. As quoted from the MineCraft Wiki;

"The number of waves depends on difficulty: There are 3 waves in Easy difficulty, 5 in Normal, and 7 in Hard."

This means to increase the amount of waves you have in a raid, you'll need to play in a higher difficulty until the raid is finished, then you could set your game difficultly back to what it was previously if you want, until the next time you want to start another pillager raid.