It could be staining, yes. There's always a possibility every time you dye unfortunately.
Semi dyes, that is true semis and not dyes that say they last longer than 6-8 washes, don't contain peroxide. Any dye that is called semi but says they last more than 8 washes do usually have peroxide. Basically, if it's one bottle it's fine, if it's two bottles it means it has peroxide.
The darkness you're seeing this morning could be just the difference in light. I do find my hair looks darker in natural light at this time of year. But it capfuls also be what's called re oxidisation. That does mean there's colour molecules left and not fully washed out, now they are growing again. You can try it once more. I would guess that it'll get you a bit lighter, but not quite as light as you'd like. You probably will still have to tone orange tones though. The orange will probably fade over time.