If the seedlings are already in full sun then I don't see a reason why you would need to shade them. Just keep them well watered and they should be fine. Why do you feel like they need to be shaded? And what type of veggies are they?

Rodney

I can't afford a shade structure made specifically for gardening right now,

Not sure there is such a thing. Why do you feel you need to be shading the garden? Late start with what specific seedlings? Do you understand that most gardeners do not shade their gardens?

Is it that you are trying to grow early spring crops now? If so then shade isn't going to help as the soil temps are what count and they are already into summer crop only temps.

Please clarify exactly what the goal is, ok?

Dave