The key is the process of the threshing floor the process to possess the promise
Ruth and Boaz at the Threshing Floor
3 One day Ruth’s mother-in-law Naomi said to her, “My daughter, I must find a home for you, where you will be well provided for. 2 Now Boaz, with whose women you have worked, is a relative of ours. Tonight he will be winnowing barley on the threshing floor. 3 Wash, put on perfume, and get dressed in your best clothes. Then go down to the threshing floor, but don’t let him know you are there until he has finished eating and drinking. 4 When he lies down, note the place where he is lying. Then go and uncover his feet and lie down. He will tell you what to do.”
5 “I will do whatever you say,” Ruth answered. 6 So she went down to the threshing floor and did everything her mother-in-law told her to do.
7 When Boaz had finished eating and drinking and was in good spirits, he went over to lie down at the far end of the grain pile. Ruth approached quietly, uncovered his feet and lay down. 8 In the middle of the night something startled the man; he turned—and there was a woman lying at his feet!
9 “Who are you?” he asked.
“I am your servant Ruth,” she said. “Spread the corner of your garment over me, since you are a guardian-redeemer of our family.”
you are a goel, a kinsman-redeemer
This was an amazing scene. We can well imagine that Boaz was indeed startled, waking up in the night as he turned in his sleep, knowing that someone was out there but not being able to see clearly because of the darkness and the sleep in his eyes.
Since Boaz had been there to protect against thieves, it must have given him quite a shock to wake up and know someone was there. But his shock quickly turned to wondering when he found out the visitor was a woman.This shows that this was not an inappropriate thing for Ruth to do towards Boaz. It was bold, but not inappropriate. Ruth understood this as she identified Boaz as her close relative (literally, you are a goel, a kinsman-redeemer).