You're on the right track but some parts of your letter could come off wrong.
- the subject should be descriptive of the topic at hand. "Kind reminder" doesn't give any information about the proposal. A better title would be "re: Proposal for ____". Also, you could reply to the original email to keep everything in the same thread.
- Saying "I would be grateful if you took a moment to look into it" is something you should have said in the first email, and is redundant at this point.
- "I will be awaiting your answer" sounds a bit pushy, saying thanks in advance or perhaps "thanks again" is enough to finish up.
Keep in mind that professors are some of the busiest people around, and if an email thread drops off the first page of their inbox, they may have completely forgotten about it. Your goal is to gently remind them your request exists and by continuing the original email thread it will show how long it's been since you first reached out without you having to say "it's been X weeks".
So, something like:
Re: Proposal for [subject]
Dear Prof. XXXX,
I would just like to check if you have had time to look into my proposal.
Thanks again for agreeing to help me with it!