because what you have is very common following vertical techniques on the breast. Your surgeon will clean up the wound if needed at your next appointment and you will continue good wound care. In the end, the resulting scar is much better than what you would have imagined. If you develop spreading redness, have an implant, or increasing drainage, your surgeon must know what is going on.
Congratulations on having undergone the breast reduction procedure. The complication you are experiencing does happen occasionally (related to blood flow/tension in the area) and tends to go on to heal without long-term sequelae, except the possible need for scar revision in the future. At your stage of healing, sometimes the area opens further before it continues to close…
I would suggest continued close follow-up with your plastic surgeon. Generally emergency room visits are not necessary or helpful. Follow his/her instructions when it comes to wound care and keeping the area clean/covered. Sometimes, removal of an exposed suture and/or any unhealthy tissue present will help expedite the healing process.
Best wishes for an outcome that you will be very pleased with long-term.