I noticed that my bike's chain is rubbing the chain stay when I use the lower gears.
The bike is new; I'm wondering what the problem is.
If the bike is new, take it back to the shop that sold it to you and ask them to fix it.
On the picture it looks like your derailleur is fully collapsed and the chain is sagging. This looks like an incorrectly sized chain (too long). A shorter chain would not allow the derailleur to fully collapse and it would keep the chain under tension, preventing it from sagging and touching the chainstay. However this is only one part of the problem. Don't hurry to go and shorten your chain just yet.
Before you shorten the chain, check what is the situation on the other end of the cassette. Check that the chain is actually long enough to be shortened without losing lower gears. If unsure, post an image of the chain shifted into the largest cog on your cassette. This is important(!). If you just shorten the chain making it too short and then attempt to shift into the largest cog, you are likely to destroy your derailleur.
If your chain appears to be correctly sized in the largest cog, but still sags in the smallest cog, it may be that your bike is equipped with the wrong derailleur (cage too short).
Looks like you have a Shimano Deore 12-speed derailleur. It looks like RD-M6100-SGS. On Shimano website I can see that that it has 51T max capacity. The cassette you have looks like Sunrace 51T cassette, so in theory should work with this derailleur if the chain is sized correctly.