From what I know, you should aim for more than 150 marks in physics and make sure you do well in your other subjects too.
St. Joseph's College in Trichy offers two shifts for their B.Sc. in Physics. The first shift is government-aided and takes place in the morning, while the second shift is self-financed and happens in the evening. To get into the first shift, you'll need a score above 1050, plus strong marks in physics.
The second shift is great too and pretty similar to the first one. If you're aiming for merit, go for the first shift with those high scores. But if you just want to get into St. Joseph's, the second shift is a solid option. The fee for one semester in the second shift is up to ?10,000, while it's about ?5,000 for the first shift.
I've also done my B.Sc. in Computer Science in the second shift, so I can vouch for it. If the first shift doesn't work out, the second shift is a reliable choice.
Last year, you had to apply in person for admission, but this year, it's all online. You need to upload your marks for them to review, and then they'll text you about the outcome. For B.Sc Physics, they'll look at your grades in physics, chemistry, and math. If you don't get in initially, you might consider getting a recommendation from a professor at the college. If there's an open spot, you'll be admitted, or you might have to wait a month. Stay patient, as they will reach out if a seat becomes available.