Based on what I’m seeing here, this should be a pretty quick fix! Feel free to correct me, but it appears this print was done with the “bottom” of the model basically parallel to the build platform. When a flat side is printed with this orientation, you got exactly the sort of results we’re seeing here.
Apologies for the strained metaphor, but imagine I’ve got a bunch of supports in an orientation that look like table legs and the printer has printed those supports just fine and now you’ve finally gotten to the first layer of your actual object(where the surface of a table would be). Now imagine instead of a hard wooden surface, we drape a very thin wet towel on top of those table legs. Obviously the towel is going to bow down in the middle simple because gravity is pulling on it, but it would only sag where there aren’t supports.
That’s essentially what’s happened here. When you print a 25/50/100 micron thin layer of still wet resin, and the only thing holding it up is some pin-head sized support touchpoints, you’re bound to get some sagging between those areas.
Long story short, the easiest way to correct this issue is just to print your part at an angle. Typically we recommend printing at 45 degrees of lean in 2 axis, so for a box, you basically want to print off of one corner. That way as it builds, the whole part supports itself the entire way up the object.
Hopefully my explanation helped a bit, but please don’t hesitate to ask if I can help in any other way! More reading on this subject specifically can be found here: https://support.formlabs.com/s/article/Model-Orientation?language=en_US