Sam Grant led the attack with 3-38 and Andy Isaacs snatched 2-12.
In their response, Steyning steadily lost wickets, despite Dave Curtis-Botting's 34, Sam Grant's 33 and Will Buckley's 19 not out, and they were all out for 136, having been 96-9.
Matt Keen took 4-25 for Goring.
Sewell said: "A few things went wrong but all credit to Goring as they played very well.
"We started fantastically, restricting them to one and a half an over for a while and getting them to 50-odd for five wickets. A couple of partnerships after this, though, helped them up to a decent total.
"I thought it was a very good total on the wicket and it would be difficult to get to. We bowled well and it was a good day for the seamers but they didn't get the luck at times.
"Goring bowled pretty well at us and it wasn't a day when we were giving away our wickets easily. They just beat us on the day and deserved the result.
"A couple of mentions have to go to Sam, who was a real class act with his bowling and batting, and Will, for some fantastic bowling, before coming in and hitting a few fours with the bat, which we all enjoyed.