To be honest, this was excellent. I can't say you don't have strengths. For a first demo reel, this was quite superb.
You had a nice range, and normally whenever people do a sad scene they unintentionally overdo it and make it cheesy, but your emotion was spot-on. (But the extended music in the background threw off some professionalism slightly. Shame on you, Sera. >:3)
The voices molded pretty well, and your voice itself is very pleasant. I can help but think that the first voice you did was pretty obnoxious, which is probably what you were aiming for.
I would recommend working on your more mature voices while still preserving your young, cute voices. As you mature, your voice will, too, and if you keep working on your older voices, you'll work out your vocal chords, since they're just like every other muscle in your body, and be well prepared for the future.
With your younger girl voices, you tend to add a hint of 'gruff/grittyness' to it, which makes it sound annoying. Try different styles and techniques to make it more cute than annoying. Also, the 'pastry shop' line was awkward, since I had NO idea what kind of accent you were going for, but it could use some work.
To be more specific- you were speaking fastish in between words like pastry and shop, as well as I think you said the phrase 'I got you many' which sounded like you tried to put an accent on there and then bailed when 'would you like one?' came around. If you're going to try and do an accent, it's best to overact than underact. I would consider the accent in there to be underacting.
All in all, you mostly know what you're doing. Awesome job!