With marks of 300 in UPTU, can I get a CS in IET Lucknow, KNIT Sultanpur, or any government college?

You have not specified your category, I will try to mention most of them and you can check your eligibility accordingly.

The examination paper has been tougher than the previous years. A 300 in UPTU means a rank ranging from 16001-25000. You can refer to this table and see which one fits your profile.

There are chances that you might get in if you fit a certain category. Also, your rank might get CS in any other government college except for IET Lucknow but if you are from the SC category, there might be a chance. Getting admission for core subjects might be harder.