Be optimistic, management may be merciful to you. However, NEVER EVER EVER let it happen again, and be sure to denote your fuel level before you lave and regularly while on the road, say every 10-20 miles or so, that way you can see if the gauge is working properly or not. I've had a similar situation in a package car, the wash didn't fill my truck for about 2 or 3 days in a row and I was still pretty green so I didn't check my gauge during my pre-trip, and by the time I noticed I had a low amount off fuel, I had to decide whether to chance that I could finish out the day, or return to the center immediately to fuel up with my helper... I chanced it, and got pretty close, but ended up having to drive about 20 miles back to the center to fill up and get back on route for 10 more stops... urrggggg....
After that, I refueld my own truck every night when I got back, and I never forgot to check my gauges again.
If you're given a second chance, do everything in your power to demonstrate to management that you can and will do the job without making such a silly mistake again. But hey,
happens, and if you have a good management and they didn't get chewed out too badly, they'll probably say to you more or less what I've said to you, and all will be well if you mind your p's and q's.
Best of luck!
Cheers