The top of my lens is slightly coming off, how to fix?

The part of the lens that is lifting on one side is called the front ring assembly. There are 3 screws that are supposed to hold it in place. Based on your pictures, it appears that there is currently only one of those screws still holding it onto the lens. The other 2 screws must have broke off or the piece it was screwed onto must have broke. How easy of a repair this is would depend on exactly how those screws broke free. If you go to a 3rd party lens repair shop, they should be more than capable of making this repair too.

As to whether it'll get worse, it's hard to say. Since there seems to now only be 1 screw holding that front ring assembly on, it is under more stress and therefore could end up breaking, causing the whole front ring assembly to fall off the lens. Also in its current state, there is a higher chance of dust and debris getting inside of your lens.