All drivers take to the track at their own and their car's risk.
There are a number of mitigating factors applied at trackdays which act as incentives for everyone to avoid collisions. These include track rules imposed and policed by organisers, eg the number of cars allowed on track at any one time (but not the gap between cars) and only allowing overtaking on the left (at Croft) on the straights, it is expected that if a much faster car approaches you that on the next available straight you indicate right and pull across (while still driving forwards yourself) to let it by. Any drivers not following the overtaking rules are usually warned once and then removed from any further participation in the day if transgressing for a second time. There are marshals positioned all around the track so infringements are easily spotted and reported; organisers do not want collisions on their safety record.
Then there is the natural concern all drivers will have regarding costly damage to their own car, and liability if you damage any of the track furniture - crash barriers etc.
Collisions are rare - although not impossible - at trackdays organised by sensible and responsible companies. The greatest risk of damage to your own car is by driving beyond your, or the car's, limits and 'going off'.
Take it easy, enjoy your track time by sticking to speeds you feel comfortable with. As the day goes on your knowledge of the track, and how much adhesion there is, will develop and you'll find yourself being able to go a little quicker, if you want to, but still within your comfort zone.
Remember, it's not a race.
] Booked ... thank you 
