I ordered a starting engine, put it on but now it keeps turning after starting. on 2001 Oldsmobile Alero

Live in Europe, hard to get the right parts. Got hold of a starting engine, looks the same as the old one. Only difference seems to me the little gear on the new starting engine, it is too long compared with the old engine.
I have a 6 cil. Alero, is there probably a difference between starter of the 4 cil?

2 answers
possibly...call the parts store you ordered it from
call supplier and ck top make sure you got the right one