Hope you're doing good in this pandemic situation.

To answer your question yes you can take part in Maharashtra state counselling for BSc nursing even when you are in first year of Bsc biochemistry there would be absolutely no problem.

But you need to understand that before you confirm the seat for BSC nursing you will have leave your seat at BSc biochemistry. I hope you know that. Yes it's ok that you filled code 5.

So they would be no problems. You don't need to worry. Also if you want you can check out your chances of getting an MBBS seat from your marks you can use our college predictor tool.

Here is the link.

https://medicine.careers360.com/neet-college-predictor