Is it a bad idea to do a second undergrad after a Masters degree?

[anna345]

I'm in Montreal aiming for McGill dentistry and my gpa is around a 3.7, so not competitive for dental school. I've tried twice to go back to do a second undergrad but dropped out after a week each time because I didn't feel motivated and didn't want to risk lowering my gpa. I recently was accepted in a Masters of physiotherapy program which I'm supposed to start in a few weeks. However, sometimes I wake up at night in panic and think to myself that I've settled and I'll never be a dentist even though it's been my dream career the last 10 years. I'm debating if I should just drop the physiotherapy program and try again for a second undergrad, but I'm scared I won't have the motivation like the last few times. I'm 28 now and starting to feel old and it's hard to see everyone continuing on with their lives. So, then I tell myself I should probably go forward with the physiotherapy degree because if I do a second undergrad and don't get in, there's no guarantee that I'll be able to get into physiotherapy again and will be stuck with two "useless" undergrad degrees (one in kin and the other in psych).
I'm debating if I should just do the physiotherapy degree now, which I'm not completely interested in to be honest, for a secure plan B and then do a second undergrad after. Or is it better to take a big risk and just go ahead with the second undergrad degree now?