Fuck!!! Caught masturbating for the first time.

I arranged with a boyfriend that we would go into town together to pick out a present for a girlfriend whose birthday is coming up. Of course, as always, he's there far too early, even though I haven't even showered yet. But he says he still has time for me to shower anyway. So he lets me get ready in peace. However, I've often imagined having a little chat with him and so I get the urge to "get ready" myself with the shower head. But as soon as I start masturbating, the shower cubicle opens and he's standing at the door. "Really embarrassing", I think. But why shouldn't I put my horny thoughts about us into action with him right away? Would you have reacted the same way?