Kitten developed a hemotoma after getting blood drawn

My boyfriend & I just got a 7 week old Munchkin kitten, about 4 days ago. We got her from a rather shady woman and were told she had gotten her first shot, but seeing as we have a 1 year old Siamese, we wanted to make sure that she was healthy so we made an appointment for the vet for Monday (yesterday). We took her to the vet because of the shot but also to find out why her eyes had so much gunk coming from them... The vet suggested that we get her tested for FIV & Feline Leukemia, which we went ahead and did. The test was negative, however they had taken her out of the room to draw her blood (which I was uncomfortable with and a bit sketched out about), they brought her back in and handed her to me and asked me to apply pressure to her back foot... come to find out the vet drew blood from the upper part of her leg and I had held pressure on the wrong spot of her leg... Now she has a big bruise (hemotoma) on her inner thigh and I am worried that it is a real problem... She has slept for literally 14 hours, but I was assuming it was because she had gotten her shots (my siamese did the same thing when he got his), she got up to eat and use her litter box but keeps going back to sleep and I am starting to worry when she was walking she was having a hard time putting pressure on her back leg... Does that mean she may have something wrong with it? I just don't know. I don't see any swelling it does feel a tad bit warm ( I have cold hands, so it may just be warm to me), and it is a half dollar sized bruise... Should I be worried? I am going to call the vet in the morning to ask them but I want to put my mind at ease before I am able to talk to them... Someone please help me out! Is there anything I should be doing? Should I apply ice wrapped in a towel to that area or just let it be? I am so worried she is just a little baby!

I am a human doctor, not a vet  but I have taken blood from humans literally thousands of times.  Haematomata are common and will almost always be absorbed with no ill effect.  They may take up to a week or more to go, subject to their size.  I can see no reason why a haematoma on a cat will be any different from that on a human but you should check this with your vet if you have any concerns.

Ice on the bruise won't make any difference at this stage.

With all best wishes,

Geoffrey