A loose zoom ring and incorrect focal length indication suggest the zoom mechanism may have slipped. One community report says the rubber grip can be slid back to reveal screws underneath, and tightening loose screws fixed both the ring play and the zoom calibration on that lens.

However, lens repair can easily go wrong if you are not experienced. Another answer strongly recommends sending the lens to Canon or a qualified service center instead of opening it yourself, because disassembly can cause additional damage and may increase repair cost if the lens is later sent in after tampering.

Practical advice: if you are comfortable doing only a very minor external check, you can inspect under the rubber zoom grip for obviously loose screws. If you are not experienced with lens repair, or if tightening anything does not fully solve the issue, stop and have the lens professionally serviced.