Hi Matthijs,
Nice to see another fellow Dutchman! Dutch bowyers are few and far between so it's good to see more people get excited about this hobby. If you want to meet any local bowyers, please let me know. Perhaps we can hook up to scrape some wood together. I'm from Wageningen.
Your bow looks pretty good, especially considering it is your first! All advice given earlier is very useful so I don't need to repeat any of that. What I will add, is that heat treating the belly of the bow is not something I would recommend for your first or second bow. While maple is a good candidate for belly tempering, it is not a miracle cure that adds ten pounds of draw weight or removes all your set. Only a well made bow will benefit from belly tempering. Belly tempering is another factor in bowyering that you could potentially screw up. Keep it simple for your first few bows.
Question, did you determine the draw weight at this point? It's not uncommon for a novice bowyer that his first few bows will come in underweight, so don't let that discourage you.
Looking forward to the pics of the finished bow!