With a double punture wound at the site, it is almost undoubtedly a spider bite.
Given the task you described you were doing that would be right in line with encountering a brown recluse. Not to scare you but just to inform, the problem with a recluse bite, is that it is relatively painless, sometimes going unoticed until things happen.
The affected area is all underneath the surface. Typically what happens is that the tissue underneath becomes necrotic and disolves. After a while what just looks like a bruised area collapses as the tissue has liquified. At that point the tissue is lost and can result in a permanant dent or sink in the skin even after fully healing.
Does the area feel warm to the touch?
I would suggest you get a doctor to look at it when possible. I realize that tomorrow being Sunday and this a holiday weekend, that your local doc may not be around. But alot of Walgreens and CVSs are starting to have urgent care available.