Almost all of the Department of Science are interconnected at the higher level and for that reason instead of in the botany department you read some chemistry courses also but I believe you would do better if you were in the chemistry department.
My grandfather cheated me😹
If I faced the same situation, I might take an aggressive move.
Yes my performance will must be good if I choose the subject of my interest. I also take an aggressive move in result of taking admission in Botany and my first semester result was very bad, but then after meeting with different good teachers of my department my interest was automatically developed towards botany. Although chemistry is still in my heart🤩