Hello, I'd like to help you with your question.
It sounds like the issue could be about control. When someone has anxiety
around their own money, it usually has to do with control. You want to hold on to something that makes you feel safe especially if you feel anxious. And if you have money, controlling it so you have enough can make you feel less anxious.
There is nothing wrong with holding back from spending money if you have big debts you need to pay down. That is actually very wise. Most people do not have that kind of control over their own money. But if you are unable to tell your partner the truth about the seminar and you feel embarrassed about your situation, that indicates there is a little more going on than just being conservative about your money.
If you feel anxious about your money, learning to let go is possible. That does not mean you go the opposite way and start spending your money. But understanding why you hold on to it to the point that it bothers you and affects your life as it does can help. Usually we get our ideas about money from childhood. If you went through a trauma, saw your parents/caregivers upset over money or suffered through abuse or trauma that caused you anxiety, that could cause how you feel now. You would want to feel secure. And if money helps you do that, that is what you would hold on to.
Therapy can also help you find out why you feel as you do. In your case, it may only take a few sessions to help you find out why and help you sort out your feelings. You may only need a little insight to help you learn to let go and relax.
You may also want to learn to relax in general to help you. Here are some resources to help you:
Keep in mind that you are already aware that this is an issue for you. That is an excellent first step and shows that you have very good insight. Just that alone will help you work through this issue.
I hope this has helped you,