I was scared too. Willow is small, actually she is over weight now, but when she was spayed she was small. I wanted to wait until she would get as big as possible and I misjudged. She came in heat at 10 mos. Two days before she was to be spayed!!!
She didn't show much but it was a mess just the same. Not too much blood but some yellow fluid mixed in, sorry I don't remember what it is called but someone on here will. She wants in my lap all the time, she's there now,
and I had to keep a blanket down on my lap all the time and was constantly wiping up after her with disinfectant wipes. Because of all the harmonal changes going on and more of the heat cycle that you don't see, my Vet didn't spay her for months after she stopped showing. My Vet is really good and she did tell me that even tho she had had one heat her chances for cancer were still very small. Good luck and yours may not show quite so much as mine did.