Yesterday, I tried installing the Ethernet cable in my room following a video on YouTube. But when I tried connecting it to the router, I found that the connector couldn’t go in all the way, only half of it could fit. Why would this happen? Are there different sizes of connectors like this? 
Usually, the size of the RJ45 plug and RJ45 device interface should be within a tolerance range and typically do not appear unable to insert the situation. It is recommended that you first confirm that the 3-prong blade of your RJ45 plug is completely pressed into the plug body (you can refer to the following picture to judge). If you confirm that it has been completely pressed into the body, please confirm that the RJ45 connectors you buy and your router come from a regular factory. Choosing to have a certain strength of the brand to buy is recommended, and you can avoid some trouble.
The reason may be that your RJ45 connectors were not properly crimped. Or if they got damaged while being crimped. I suggest you check if the crimping tool and the connector match or use better-quality of them.