Can you have too much blown insulation in your attic?

Yes, you can have too much blown insulation in your attic if it is installed in a way that creates problems, though from a pure thermal resistance standpoint more R-value is generally better up to about R-60. The most common problem with too much blown insulation is blocking soffit ventilation, when insulation is blown over the top plates and into the eaves it covers the soffit vents, preventing fresh air from entering the attic and causing moisture buildup, mold, roof deck rot, and ice dams in winter. Another issue is covering up electrical junction boxes, recessed can lights that are not IC rated, and bathroom exhaust fans, which creates a fire hazard because those fixtures need air space to dissipate heat. Excessive weight can also sag drywall ceilings, especially with heavy cellulose piled 18 to 20 inches deep over 1/2 inch drywall with 24 inch on center joists. Over-blowing can also bury attic access, make future work difficult, and if insulation is blown too light and fluffy to look thick without meeting density requirements, it will not achieve its rated R-value despite looking deep. So you should aim for the target R-value depth per manufacturer charts while keeping soffit vents clear with baffles.