A 3% profit margin isn’t modest, it’s catastrophic. With a their heavy capital requirements and massive technology lead they should be banking 30%. 3% says please shut us down first time we have a bad year.
However spacex could easily survive off 3% profit for now, as long as they still keep collecting all their used rockets. I only remember them launching one used rocket so far which was successful, and presumably they'll work out any remaining glitches and start using the others.
There isn't a space launch company on the planet who can launch anywhere near the cost of SpaceX and make a profit. That's without counting re-usablity, mind you. With re-usablity SpaceX should be able to slash prices by at least 50%, though they shouldn't until the market forces them to. Instead they should be re-investing those profits into Raptor and the BFR.