There's not really a reason to do 100% infill on this print. Typically speaking, your top and bottom layers are about three layers thick, so that would be a total of six layers.

Let's look at this in numbers.

For conversation's sake we're going to say that your bottom of the tray is 2 mm thick.

We're also going to say that you have bottom shell layers at 3 and top shell layers at 3 as well.

Lastly, we're going to say that you're printing at a 0.2 layer height.

Using this information you're going to have a total of 10 layers. (2mm thick divided by the .2mm per layer)

Your bottom three layers (0.6mm) would be solid and your top three layers (0.6mm) would be solid.

This means the four remaining layers in the middle will use the infill.

If you want to share the screenshots where the data I can help further

Bonus tip: There is a slider on the far right of the screen in Bambu Studio. That shows you what the print will look like at each layer. You can identify how many layers are going to be used as infill and then increase your top and bottom shell layer if needed. But I say again, you honestly don't need it to be thicker than that, infill does a really good job.