OOps!I posted this after problem solved.I will leave it up,works with a metallic guard.I have made the same mistake.Slow down!!
Good news,absolutely no damage need be done to your lower.No drilling,tapping,etc.
Order another trigger guard and pin.
The Blind hole is actually only drilled through one side,the other tab has no hole.
So,the trick is,the dremel abrasive cutoff wheel.I use a Foredom motor.You slice the corner off the trigger guard,cutting through the pin.This would be slicing off the corner you drove the pin into.You are only cutting the ejection port side corner off the trigger guard bar,and cutting the pin as you do it.Wear eye protection,put the lower in a vise,use both hands to keep your die grinder stable,and watch what you are cutting.If you want,slip a piece of feeler gage between the guard and the mag well as a shield.Be very carefull not to cut into the mag well.Once that corner is free,the rest of the guard will swing down,and then the corner and pin can easily be removed.