To get a straight man sleeping with a gay guy is not at all impossible, just as you might be thinking.
First, I think that is your exact problem - you load yourself with too many negative thoughts, leaving very little space for an action plan that will actually help you nab a straight man into bed. Truth is, all emotions grow in size when practiced regularly. When you practice not getting a straight man sleeping with you, it happens undoubtedly, but otherwise, the possibility is the same and leave better results. The choice is always yours as always.
The sex is actually the end part, and everything that you do prior to that spells the outcome. Confidence is the key. When you have a can do attitude, you will be more relaxed in your approach, making it natural and not the bit awkward. You can now focus on creating the best atmosphere to get a straight man noticing all your good qualities aside from worrying to death what to say or what to do. When you doubt yourself, everything seems forced and no matter what you end up doing, it will appear odd because the energy you put into it is negative.
People normally gravitate towards others who are sure of themselves and know exactly what they want. There is no difference in trying to get a straight man sleeping with you. Show him that you are a cool person that is a lot of fun to be with and give him every reason there is why he would choose to spend time with you. When you are calm, collected, and your natural desirable self, the sex will come out eventually.