Asked Straight Friend to Show Me His Stuff, Feel Guilty For Asking?

A friend and I were having a close talk about life and getting to know each other better. We were having about sex and what not, confiding in each other stories we have about ourselves and other people. One topic led to another, and I asked how big his dick was. He told me 8 inches, which is crazy, but possibly believable because of his height and overall figure. So I said prove it, wanting him to pull it out. I'm gay, and we're still close friends, so I didn't have to worry about him thinking I was gay. He said no, but he didn't seem mad about the question. I kept trying to get him to show me, and it overall didn't happen. We talked for some more, and then we got Starbucks, and I took him home. Honestly, I really did want to see it, especially to see if it was truly 8 inches. Nonetheless, I feel severely guilty. He's straight, and that's his private business. Of course I still would love to see it, but I just worry I did a bad thing. Like I said, he does seem fine, he didn't seem severely weird-ed out, he laughed at points, and maybe I'm just overreacting. I do like him a bit, but he's just a close friend and I know that's all it's going to be. My question is, how can I get over this guilt? Should I apologize sincerely for even asking in the first place, or should I just let it go and pretend nothing ever happened?