You are right that "regressive" is the opposite of Progressive and that has a very different connotation than conservative. In fact "reactionary" is more what Republicans have become rather than conservative.

I am both liberal and progressive. Looking historically, I probably fit liberal better simply because some major progressives in the past were anti-evolution and such. By contrast, I can see almost all major advances in America have been liberal advances. But the overall philosophy of progressivism (and, for that matter, populism which has even different connotations) is something I like.

In the end, of course, they are all labels. In truth I get along with conservatives better than I do EITHER Greens or reactionaries. There are some things I am pretty leftist on but there are some I am conservative on. But sometimes choosing labels is convenient, and I am comfortable being labeled either liberal or progressive.