Well, there are two fresher's parties organized at PEC Chandigarh. One is the hostel fresher's where the dress code is based according to the theme of the party and they will tell you the dress code before a day or two.
Another is the branch wise fresher's party where there is no such mandatory dress code and one can wear anything they like. Yes, many people tell that boys should wear western formals and girls should wear a western dress to the fresher's party, but these are all rumors and it is not compulsory at all.
Many people prefer wearing formals but you can choose to wear whatever you are comfortable with. You can go to the party wearing party casuals and it is perfect wear as these clothes look good and are also comfortable too unlike formals. Some people even attend wearing casuals too.
It is completely your choice to choose your dress for the fresher's party and no one will judge you based on your clothes.