Welcome to HCM.
You had protected sex all the time. Slipping of condom during taking the penis out was quite common and the chances of HIV transmission is still negligible. Your terminal portion of the penis is more vulnerable for abrasions and HIV entry. As it is covered, your chances of getting HIV is very remote.
So you need not worry. Forget about the incident and count your days ahead for your marriage. There is no question of stopping the marriage.
You can have your HIV test
boldly to see a negative result before your marriage, 3 weeks after your risky sexual act with either P24 antigen test or HIV DNA PCR Test or a COMBO/DUO
Wish you a good luck.