Ive read online that premature babies have a 30-50% higher all cause mortality rate compared to those born full term. i was born at 28 weeks and i have adhd and tourettes. does this mean ive a higher chance to get chronic illnesses?

Research confirms your inquiry, Prematurity is associated with learning and motor disabilities along with hearing and visual impairment. Females are more affected.

I would avoid using "generalities" when applying them to pre-term births. There are many variables involved and life expectancy should be individualized to the factors for that individual. Even with your neurological conditions you should not live life expecting to die before any given age. Long term health conditions also occur at higher frequency for many reasons not related to prematurity.