What would you like me to tell you? You're the one who's feeling anxious--obviously about getting married. I can't fix that for you; only you can do that.
You need to examine your feelings about this impending marriage and why you're feeling anxious and afraid. Almost everyone goes through some worries right before making this big commitment. Obviously, this is now getting in the way of your
sexualCauses of sexual dysfunction
Erection problems
Female sexual dysfunction
Sexual problems overview desires for your partner.
You've also created a self-fulfilling prophesy: once you didnt' get an erection the second you thought you should, you began to worry; and now that worry is part of your sex pattern.
In addition to examining your feelings about your upcoming marriage, I highly recommend you read the book, "The New Male Sexuality," by Bernie Zilbergeld, Ph.D., widely available online, both used and in paperback. This book has helped thousands of men to better understand their sexuality and their emotions. Best of luck to you. Dr. J
Thinking about your problems sometimes just makes them worst... sit back and they begin to lighten up until you understand them better.
Also, you just have sexual performance anxiety... check this out, should help:
"Exercises to Strengthen Erections, Overcome Sexual Performance Anxiety, and Increase Sex Driveā¦"