It should fit, but it is pretty easy to bounce off that entrance. It isn't open immediately (lasers, iirc), but when you're told to enter, you should be able to.

Interestingly, you can take a larger ship and get through small holes by turning through them - I was able to get through everything in a Deimos because I felt like being silly (turns out that narrow, long passages are more inconvenient than tiny holes, 'cause an oversize ship vibrates, making laser traps very hard to navigate).

Actually . . . you could use that technique with a small ship too, I suppose. Face into the hole, push against it, then slowly turn to the side, adding some strafe thrust once you've turned 30 degrees or so, shifting to entirely strafe thrust as you approach 90 degrees. You should pop though, since even the much larger Deimos can do it. Or just push into the hole and wriggle around by turning and strafe-thrusting all around - that first hole is the only one where the Salty Dog has any chance of jamming.

(Unless you mean the small hole at the last relay, once you're inside the tunnels and have destroyed the others - that one you *can't* fit through, you just shoot the relay through it. The above advice assumes that you mean the initial entrance to the tunnel system.)