The size of a shoe doesn't always tell the whole story. While a shoe may "fit", your comfort level can still vary. If you need some extra breathing room, put a Ziploc bag filled with water in your shoe and toss it in the freezer.
As we all (hopefully) learnt in school, water expands when it freezes. That means a small bag filled with water will stretch your shoe a little bit as the ice forms. While you should be careful not to overstuff your shoe -- lest you risk tearing it -- a little extra give can mean the difference between comfort and searing pain all night long. When you're done, break the ice out of the shoe. As tips blog Better Remade explains:
I typically freeze them overnight, take them out in the morning, break out the ice, and then repeat once more and leave them in for the next day and night for a little extra stretch. Do not let the bags melt inside the shoes, that will lead to wet shoes, and might ruin them. Most of the time I can wiggle out the ice bag, or I break it out with the end of a knife.
This is yet another tip in the surprisingly specific category of putting-shoes-in-the-freezer tricks. Just be careful not to let the bag rip when you're placing the water in. And, as the source points out, it's better to break the ice out of your shoe, as the expansion could rip the bag. Allowing it to melt can damage your shoe as well.