You may have taken the whole ½" diameter of the bit away from the edge of the jig. In fact, if your baseplate is 6" and the bit is ½", then the edge of the baseplate is 2 3/4" from the edge of the bit. That is, 3" from the centre of the baseplate and bit to the edge of the baseplate, minus ¼" from the centre of the baseplate to the edge of the bit. Your stop block needs to be 2 3/4" from the edge of the planned recess. Measure this with a ruler before you set out the edges of your jig.
I'm not slow, I'm pacing myself!
Isaiah 44:13 Another shapes wood, he extends a measuring line, he outlines it with red chalk. He works it with planes and outlines it with a compass...
Usual kit: Table saw, band saw, dual base router and table, lathe, various saws, planer, sanders, and a multitude of hand tools.