I am 25 weeks pregnant. i quit smoking when i found out at 4 weeks then relapsed a few days ago and smoked a total of 3.5 cigarettes before stopping again. will this amount have long-term effects on my baby like adhd, immunity issues, asthma, etc?

As described, the exposure to inhaled cigarette smoke and nicotine should not significantly influence fetal health, but continued use of tobacco products can.

I doubt any long term effect if you can stay off nicotine. The research on continuous smoking does indicate a smaller baby with potential problems, but sporadic exposure is less likely to have a predictable impairment. To me the worst factor is having that exposed kid, with the known difficulties, grow up around smokers & decide it is okay as a teen or adult. Multigenerational problem.