The rule of thumb is (depending on the typing of gathering) your curtains should be 1.5 x the length of your curtain track/pole (not the window size). These measure 260cm in total, 185 x 1.5 = 290ish - you should be OK but it depends on your track and the type of pleating etc at the curtain top.
it depends on the curtains, mine are eyelet on a pole and designed not to look gathered when drawn. If they have tapes and draw strings then they aren't wide enough IMO and yes, will look stretched.