The sharpest pin-hole photographs are made using the largest film the pinhole will illuminate.

At 250mm (10") focal length you should be thinking of 11x14 or 16x20 film - not 35mm. Contact print your 35mm negative and stand back from it as if it were a 16x20 print and see if it seems sharp now...

'Telephoto pinhole' is a bit of an oxymoron.