Dogs look at open backed steps differently than we do. Had the same issue with out rescue chow / lab mix. he was terrified of going up he steps into out truck camper (we have 5 steps not 3). Soon as I cut pieces of Masonite to block off the 'see thorough' part of the steps, he went right in. We put his food dish in the to entice him a bit too. he's a big guy, 118 pounds so the steps flex a bit when he uses them but he pays that no mind.
I think if you block off the 'see through' part, he'll go in, especially if 'dinner' is inside. Dogs are especially food oriented. Food and routine.