What did you do with the liter of wine?? Next time, bottle the extra and throw it in the fridge.
Maybe it's me, but you would do well to make sure you're properly degassed during the 3 months in the carboy. If it's not, you'll need to make an alternative plan before bottling (like degassing in a vacuum, or moving your wine to a warmer spot for another 3 months).
Use an airlock. Just keep track of the level inside the bubbler. I use vodka in mine, others use KMeta solution. But check it ever few days.
Adding a bit of similar wine to top off is common. You didn't do anything bad. But, next time, when you need to top off - go to the fridge and pull out that bottle you put in there... Yeah, use that first.
You can rack it off (what should be) the fine lees. But at the end of the three months, you'll need to dose w/KMeta before you bottle (dose and rack every three months seems to be the rule of thumb).
Finally - relax. You're going to be fine.
