Spindly tomatoes

I grew some tomato seeds, two kinds, on a heat mat under a grow light. They’ve just got their second set of true leaves, and I’m wondering if I can bury them deeper now. They don’t quite stand up by themselves, but bend to greet the sunrise and sunset. I may have been too slow to put them in full sunlight, I’m acclimating them (too) slowly so they dont’ burn up.