can i do B.tech after CET exam instead of JEE for software engineer

Hii

Yes. You can pursue your B.Tech degree by writing CET and getting a good rank in it.
JEE Mains is a national level entrance exam for the aspirants seeking admission in IITs, NITs and CFTIs. These are the top and prestigious institutes in India.
As JEE Mains is a national level entrance exam, cracking it is not a cake walk. You have to be the top among the top candidates. If you want to get admission into IITs or NITs you should have more than 98 percentile in JEE Mains. You need a lot of practice for this.

So if you are not well prepared for cracking JEE Mains, you can also give CET of your respective state. Cracking CET and scoring well in it will fetch you good ranking. If your ranks are excellent then you can easily get admission into the college and branch of your choice depending upon your rank.

Cracking your state CET won't help you in getting admission into IITs, NITs or CFTIs but you will be getting admission into a college in your state which accepts your state CET ranking. You can get into Software Engineering if you have good scores in CET.

So whichever exam you are aiming for, just put all your efforts and score well in them. Getting a good college after a good ranking should be your aim. After all your field of interest matters.

Hope this helps
All the best!!