Sure.
First ask yourself what you are nervous about? (and there are understandable reasons why a perosn would be in this situation)
Is it the hidden fear of what if she says no? The idea of it being a life long commitment? Etc. Some nervousness is understandable, as no intelligent person would go into this without having thought this through.
You are nervous because of a concern, or fear - nothing more - That is the first thing to know. Once you find the core of it, look at it from different angles. What I do when faced with something nerve taxing, is ask - “What is the worst that could possibly happen?” At first, this is uncomfortable, but then after a bit, the nervousness goes away. It is hte unknown we fear - little else.
For each fear, do not ask “what if” questions, ask “How would I solve this?” Do not let yourself get into endless loop questions - they do not help. Ask yourself solution questions. Once you have these answers, do not look back. You have a plan, and trust in that. If your mind want to run to the negitive, try and change this to what you will both gain when you are past the proposal.
Beyond this, pull a Zen/toist - be in the moment - Only that moment. Not the future, not the past -Enjoy the experience.
Cheers