How is it that, although the Creature clearly warns Victor that he will be with him on his wedding night, Victor goes ahead and marries Elizabeth, showing no concern for the danger in which he will be placing his bride?

There appear to be two likely reasons for Victor's behavior.
First, Victor believes that the monster is only targeting him, not Elizabeth. Second, Victor believes that he can repel any attack the monster unleashes on him.
The text tells us that Victor does not once suspect that the monster will harm Elizabeth:

"I WILL BE WITH YOU ON YOUR WEDDING-NIGHT." That, then, was the period fixed for the fulfillment of my destiny. In that hour I should die and at once satisfy and extinguish his malice. The prospect did not move me to fear; yet when I thought of my beloved Elizabeth, of her tears and endless sorrow, when she should find her lover so barbarously snatched from her, tears, the first I had shed for many months, streamed from my eyes, and I resolved not to fall before my enemy without a bitter struggle.
Great God! If for one instant I had thought what might be the hellish intention of my fiendish adversary, I would rather have banished myself forever from my native country and wandered a friendless outcast over the earth than have consented to this miserable marriage. But, as if possessed of magic powers, the monster had blinded me to his real intentions; and when I thought that I had prepared only my own death, I hastened that of a far dearer victim.

Victor is resolved to fight the monster to the death. He prepares emotionally for a "bitter struggle" but cannot imagine that the monster would stoop so low as to hurt a woman. In their exchange, the monster begs Victor to create him a mate. For his part, Victor refuses. He balks at the idea of creating another monster that is equal in wickedness to that of the creature before him.
Upon hearing Victor's answer, the monster flies into a rage. He promises Victor that he will exact his revenge on him. However, Victor thinks that he is ready for anything that the monster will try.
Victor has totally misinterpreted the monster's motives and behavior. However, either by naivety or overconfidence, Victor chooses not to take precautions. This is why he goes ahead and marries Elizabeth, showing no apparent concern for the danger he will be placing his bride in.