Can you also upload a picture of the front sprocket and rear sprocket please? so we can see the close up of their teeth , then I will have better advise if it wise to replace just the chain or not.
general consensus is that a chain should be replaced with the sprocket , but because it is a 125 running on a 520 sprocket, you “may not” need a rear sprocket yet but the front sprocket is more critical as it wears down much much faster.
Also report how many miles you have done and what chain lube do you use ? how often do you lube it ?
Sometimes not lubing the chain after it rains , makes it wear out a lot faster , it’s just how mother nature is vs naked moving parts.
If you do a LOT of miles every day, I could do you an X-Ring chain next time but we can discuss that privately via email.
For now, just show us here what your sprocket teeth look like and report back “miles , lube product , how often etc.”