The count of 603,550 shows the same number of qualified men as mentioned in Exodus 38:26. Exodus 12:37 and Numbers 11:21 give an approximate number of 600,000.
People have interpreted these numbers in different ways:
The numbers might show the actual size of this army (see Exodus 1:9–10).
The numbers might be symbolic. A later editor might have estimated, or might have misunderstood while translating.
See also study note on Exodus 12:37.