I dropped a table in Oracle, how can I retrieve it from the undo tablespace?

I dropped a table in Oracle, how can I retrieve it from the undo tablespace?

I accidentally dropped a fairly large table -- recycling bin is not
enabled. I'm fairly certain the data still exists in the UNDO tablespace,
but I'm not sure how to get it out. I recreated the table exactly as it
was before it was dropped -- the structure is exactly the same. However,
when I attempt to flashback the table, I get this error:
flashback table tablex to timestamp (systimestamp - interval '120'
minute); Error: 01466 DBD::Oracle::db do failed: ORA-01466: unable to read
data - table definition has changed
Any idea how I can overcome this error? From all of the searching I've
done, it seems as if it believes the table is not structurally the same as
when it was dropped.
Thanks so much!