I can fit (16) 3 gallon pots on 24 cm saucers into a 100cm x 100cm x 200cm tent.
or
(9) 5 gallon pots on 30cm saucers
or
(5) 10-15 Gallon Pots on 40cm - 45cm saucers(for photos, not autos. Would be overkill for indoor autos)
Not a lot of elbow room when packed that tight but its doable.
If...
For your auto I also wouldnt start it in a solo cup. Germinate and plant in its final 3 or 5 gallon pot. The transplanting from solo cup to pot is going to cause the plant at least a few days of stress. You dont want to lose any days for any reason with autoflowers other than perhaps...
imo, they should be a lot bigger at 20 days. Probably 3rd or 4th node. Also your 1st and 2nd node leaves are very small which will make it hard for the plant to grow quickly.
For comparison the plants below were 17 days old. Planted Jan 12, picture on Jan 29. The one just below the...