I haven't done Biology / Chemistry / Physics before...

As always, how much of a concern this is will depend almost entirely on what you are aiming to get out of your HSFY year. To simply pass the courses, you will certainly have a bit of work to do, but you should be able to get by if you work diligently and take advantage of the resources offered by the University. If you want to gain high enough marks to obtain entry to the professional courses, it definitely can also be done. However, you will need to really commit yourself to the cause from the outset and put in long hours to make up for the lost ground. Chemistry and Physics in particular assume a lot of prior knowledge, and, in our opinion, make very minimal efforts to accommodate those who don't possess it. You will probably need to consider private tutoring if you have already missed the opportunity to take one of their "catch-up" courses over summer, and want to move yourself to a level of understanding which will allow you to compete for a place in one of the professional courses.