Mate there is a huge risk that the frame might give way.
What happens if that frame breaks when your hooking into your favourite high speed corner or going down a rough track at speed.
I'm sorry to be blunt but not only is the tube work you've done not up to scratch but your welds are no where near good enough for frame work. From the pics it looks like you have a lot of slag contamination and inconsistant penatration which will premote sudden cracking through the weld and as your frame design is relying on weld strength and not trianglation then you probably wont get a warning of a stress fractures apear but a complete and sudden faliure.
Please for your own safety please have a fabricator look at it and design some proper down tubes.
You've already done all the hard work it would be easy for a fabricator to knock up some nicely bent down tubes and weld them in there for you.
Sorry about the bad spelling.