Have you considered taking a non-thalys train to Antwerp? There are hourly connections (leaving at :37), which take about half an hour longer and require a change in Rotterdam, but they might be the better option, if you're unsure whether you can catch your train (please note, that I needed to wait for almost half an hour for my bags to arrive on my last arrival at AMS). I have to admit that I'm absolutely not a fan of Thalys, and might hence be a bit biased, but I would definitely look at the other options.