I have paid the hotel room fee in advance, but the hotel showed in eLong that the price on the day I checked in changed again. Do I need to pay more?

No, you succeeded ahead of time. No matter how much they increase the price, you don't need to increase it. If you only book for one day, you need to increase the price the next day. This is also the reason why many customers will book rooms more than one month in advance on holidays, because holiday hotels will raise prices more or less, especially scenic hotels, and it is often hard to find a room!