Hey there ! First of all congratulations on your offer to study Quantity surveying , no matter which one you decide to go with they are both good STEM choices.
If Quantity Surveying has always been your passion and you want to pursue that specifically then , it's advisable to accept the first-year offer for Quantity Surveying. Pursuing what interests you directly aligns with your career goals and ensures you focus your efforts on developing expertise in your chosen field. Be aware that studying civil engineering could lead you down a path where you could be a quantity surveyor in the future , you can even do a masters in Quantity surveying with a civil engineering undergraduate degree but I don't think it is easy to make the transition the other way around from studying quantity surveying then trying to work as a civil engineer. Ultimately it will come down to what you want to do but I would say weigh your pro's and con's and consider every possible career path you can change in the future.
I hope this helps .
Cece
Energy Engineering Student
De Montfort University