I had a tick on my stomach last night and pulled it out. All of it came out including the head. I killed it and kept it. Now what?

Probably that's it. In all likelihood nothing else is required. However monitor the site for possible infection ( redness, swelling, drainage). Cleansing of the wound with an antibacterial may be warranted. I am not aware of lyme disease being prevalent in your area but you may want to look this up on the public health department website in the area in which you believed you sustained the bite.
Probably OK. You've taken out the tick, so you're probably ok. Even if it was a lyme disease-carrying tick, it would have had to have remained attached to you for at least 24 hours to transmit the disease. If you don't know how long it was attached, you should see your doctor for lyme titres (one now, one in a couple of weeks) to be sure.