Skinny dipping

Me and my wife always wanted a pool, so we finally broke down and got one. There is nothing like coming home from a long hard day of work and jumping in the pool and relaxing with a nice cold adult beverage. We have a pretty normal sex life. Nothing to kinky, especially since my mother in law lives with us, so it kind of took me by surprise when my wife came up with her devious plan. One friday evening i came home from work and stuck to my usual routine of getting a cold beer and changing into my swimsuit to get ready for a dip. As i was getting undressed, my wife walks in already in her swimsuit. Wr start making conversation about how work is going and pretty soon im naked looking for my swimsuit. I realize i left it in the laundry room and ask my wife if she minds going to get it for me, but to my surprise she responds with " why dont you just go naked?" I say " really, dont you think your mom would mind,?" She says " i dont know? I bet your to scared to do it anyway. Ill give you a towel. You can wear that when you walk by her. She won't know your naked under there. Then when we get to the pool you can sit on the edge before taking your towel off" i say are you actually serious and before i know it she leaves the room and cones back with a small towel and says " i dare ya" i take the towel and wrap as much of it as i can around my waist, but its too small to go all the way around i say " now how is she not going to know im naked? You can clearly see like three inches of my bare thigh." My wife says" just put the opening on the side that she wont see" so i adjust the towel to where my thigh will be showing on the opposite side of where my mother in law will most likely be looking and i prepare myself mentally for my butt naked excursion. The thought of my naughty adventure is starting to give me a semi hard on so if im going to do it now is the time. If i wait much longer there will be no way to hide the fact that im naked under the towel. I agree to do it and start walking towards the door. My wife shrieks with excitement. Everything is going as planned until we get to the living room where we thought my mother in law would be sitting. Thats when we realize that she is in fact outside sitting by the pool smoking. I look at my wife and say no way this is happening now. She says "aww you big baby, are you scared my mama is gonna see your penis?" With that i man up and say "fuck it, ive come this far" i open the door and walk outside. I still have the towel gap facing opposite of my mother in law, but now i have another problem. My penis is rock hard and straining against the towel. I say hey to my mother in law and politely ask her if she wants to join us for a swim, knowing she would say no which she did say no. I noticed that when i was speaking to her, my bulge caught her eye. My wife comes outside and starts talking to her mom which gets her attention long enough for me to get to the edge of the pool. When i noticed she wasn't looking, i dropped my towel and slipped in the water. It felt so awesome being there butt naked with her sitting just ten feet away and not knowing. When my wife came over to get in i could tell she was surprised that i went through with it. My mother in law eventually goes back in the house while me and my wife swim, me still remaining butt naked. After about 20 minutes of swimming, my mother in law comes back outside with a plate of raw hamburgers and sits then on the gas grill. She starts messing with the grill but cant figure out how to light it. The whole time im panicking inside, because i know where this is going, and sure enough she asks me "can you please come ahow me how to light this grill?" I think to myself, oh shit! What do i do?