This is either a tuberous or a Reiger begonia (I suspect the latter). They look so beautiful in the store because they were grown in ideal conditions and then get stressed out due to the move and then growing in less than an ideal environment.

First thing to do is monitor your watering. If the soil stays wet then it will eventually rot and die. Let it dry out some before watering again.

Move it outdoors to get as much fresh air, heat, humidity, and bright light as possible. This should make a tremendous difference. If you can't do that, then put it under bright lights indoors and hope it responds.

Typically these would be treated as annuals but you want to make them go at least for the growing season.

hcmcdole helped/encouraged me in saving my Sinbad. It looks like yours is outside. Maybe it needs just a tad bit of sun but not too much, early morning or late afternoon, but could be different for your variety.

It's too early to fertilize with anything, but I did some research last year, not sure, but they might prefer acidic soil. I've been giving mine a little Miracid (pot strength) now and then also some Osmocote. But I wouldn't want to do it this soon and possibly stress it more.

Sure is a beautiful one. They look so nice in the photos. The main leaves look healthy still, but if that is new growth, it doesn't look too happy, and the blooms have to be disappointing at this point.

Good luck with it. Sometimes when I put a new plant into a larger pot, it takes awhile to adjust. I usually clean the pots as best I can and run them through a bucket of bleach water and rinse well, usually don't if it's a brand new pot.