Will anything happen if I start a blister with contraception 2 days later?

You did not write what drug is meant, but the described delay is very unfavorable. Starting a contraceptive blister two days later should be treated exactly the same as skipping two active tablets in the first week of use. In cases known to me, the delay in starting the blister causes the patient to lose protection against pregnancy, also if she has already had intercourse (e.g. during a 7-day break). If two active pills are missed, the contraceptive documentation refers the patient to the doctor. I enclose additional information: https://www.gdziepolek.pl/artykuly/jak-prawidlowo-stosowac-antykoncepcje