It sounds like one (or both) of two things may be happening. Most crust recipes tell you to add water just until the dough comes together. It’s pretty easy to be tempted to add a little too much water, since it makes the dough feel easier to work with (and we’re only talking teaspoons here – no major gaffes on your part). Once the heat of the oven hits the dough, though, the excess water will literally vaporize, leaving you with less crust – so that could be part of it. You might try working with a tad less water and see if it helps.

The other trick is to really make sure you’ve rolled out the dough large enough that you won’t have to stretch it one bit. Stretching dough will get you nowhere. It’s like cramming yourself into too-small spandex – it may seem like a clever solution when you’re getting all tarted up (ba-dum bum), but it will leave you with unsightly bulges and sometimes even some naked spots at the end of the day. To avoid these and other reputational disasters, start by rolling out the dough to the point that it is one to two inches bigger in diameter than your pan, so that you will have enough excess to work with. Then, when you ease the dough into the pan, be sure to tuck it thoroughly against the bottom and the sides and along the seam where the sides meet the bottom – there should be some right-angle-age going on. You should almost err on the side of compressing the dough a bit rather than stretching it at all. I think there is so much talk about not handling your dough too much that people are getting afraid to even touch it. You do need to use a bit of pressure to be sure there’s no gap between the dough and that “corner” around the perimeter of the pan.

Hope that helps. Report back when you try again! And remember, ugly tarts can be tasty tarts, so don’t worry too much.