I need help as soon as possible
Editor's CommentI think it is very unlikely that you could be pregnant if the tip of your fiance's penis did not go near your vagina. Technically you can get pregnant from precum but it would have to be in the vagina or very close to the entrance. The only query in my mind is how sure you can be while having anal intercourse that sperm has not leaked out.
However I think it is more likely that you are worried about what has happened and this has delayed your period.
If you choose to continue having some form of intercourse it would be worth you getting some form of contraception, and your fiance would be advised to use a condom during anal sex to protect him from infection.