The hole is a slightly too big for the motor's shaft. I thought about hot gluing them together.
Which piece is the robot? This is not a robotics question.
I have to assume since you are asking a question that shows a lack of fundamental mechanical understanding, that for its intended use, precision is not a requirement.
In that case, wrap the motor shaft with some tape until you have the tightness you are looking for.
A more appropriate fix would be some form of adapter.
For any real application, the propellor size is almost certainly incorrect for that motor. A gear reduction unit is needed.