I have a terrible dental phobia and I'm due some fairly heavy work in a couple of week's time.
I was meant to be going in today so the dentist prescribed me 5mg of diazepam to take the night before the appointment and another 5mg to take 2 hours before the appointment.
I took the diazepam as prescribed but unfortunately one hour before the appointment the dentist called to reschedule due to a last minute illness.
However, this has given me a trial run of the diazepam and admittedly I'm not filled with confidence.

I slept well last night but I sleep well generally anyway. After the 5mg dose this morning I felt a little heavy headed for around 15 minutes, around half an hour after I took the dose, but that quickly passed and other than that I didn't feel any different at all. The anxiety is still there and I've felt bright and alert all morning.

It's been around 4 hours since I took the 5mg dose and it felt like I barely even noticed I'd taken it.

My appointment has been rescheduled to take place in around 2 week's time and they've told me they'll prescribe the diazepam in the same way again but I'm really worried it isn't going to help me after this trial run.

Would it be better for me to save the dose from the night before and instead take 5mg on waking and 5mg one hour before the appointment? I feel like this would be more likely to help but I don't know if this is safe or advisable.
I haven't taken diazepam before today so I don't have any experience with it.

I don't have the option of IV sedation as my dentist doesn't offer it and the sedation clinics near me aren't taking on new patients right now due to the pandemic so I'm stuck with oral sedation :(

I've tried to get over my phobia but I had a traumatic experience as a child and just can't seem to get past it.

Advice appreciated, thank you!