As part of casting the spell, you can form a circle on the ground with the blood used as a material component. The circle is large enough to encompass your space. While the spell lasts, the summoned demon can’t cross the circle or harm it, and it can’t target anyone within it. Using the material component in this manner consumes it when the spell ends.
While it doesn't specify where the circle is, the obvious intent is that you're drawing it around yourself.
That said, if you had cast mage hand and used it to hold the vial of blood, would it be possible to draw the protective circle at a distance of up to 30ft?