It's completely understandable to feel a bit upset or inconvenienced when your therapist accidentally mixes up your time slot with another client's. Having a disruption in the therapeutic routine can be disconcerting. However, it seems like your therapist recognized the mistake, took responsibility, and showed remorse by being extremely apologetic. Additionally, offering you dessert during the next session can be seen as a gesture to make amends and demonstrate that they value your time and the therapeutic relationship.
As a client, your feelings and reactions to such situations are valid. If you feel comfortable doing so, it might be helpful to communicate your feelings and thoughts about the mix-up to your therapist. Open communication can strengthen the therapeutic relationship and help your therapist better understand your needs and preferences.
Ultimately, your take on the situation should be based on the overall quality of the therapeutic relationship and the progress you're making in therapy. If this mix-up was an isolated incident and your therapist has been consistently supportive and helpful, it may be worth acknowledging their efforts to make amends and moving forward with the therapy. However, if you have concerns about your therapist's punctuality or other aspects of the therapeutic process, it's essential to discuss these issues with them to ensure your needs are being met in therapy.