My number one school (Washington Uni in STL) is not a partner with this program. And my problem is that if I get matched with these school then I have to go, but then that would mean that I can’t apply to WASHU ED because what if I get matched to a Questbridge partner college? 
I don’t know if I should risk not applying ED to WASHU and do this program instead. But the only schools I’d want to go to in Questbridge are the impossible to get in Ivy Leagues.
if you are a strong applicant, Questbridge is more of a boost than ED
If you do Questbridge only choose schools you would want to go to. And you really have to decide if the amazing scholarship would be worth going to a second choice school (that in reality would be pretty equal to Wash U assuming you only pick top schools). Having that guaranteed $$$ to a really top school might be worth it to you but if not going for ED isn’t a horrible idea as Wash U is generous but you would probably have some loans to pay back after college.
There are four schools in Questbridge that you can match too that don’t require attendance. Yale, Princeton, MIT, and Stanford, if you apply only to these schools and match you could attend or wait until WUSTL comes back with ED decision.
Not sure if you can apply ED to WUSTL and Questbridge though.
OP I would suggest applying to QB. Assuming you become a finalist, you can choose NOT to RANK. Apply ED to WUSTL – important!! – only after running the net price calc with as many variations in income as might affect your family and making sure that if you are admitted you can afford it.
Be aware that in doing so you are skipping over the chance at a full scholarship (no loans or parental contribution) through a QB match. You would have to be okay with knowing that. Our elder son did that with his favorite school. It is a QB partner but he applied single choice EA through Common App instead. In case it didn’t work out he had his Plan B…and then a Plan C.
If you get rejected or deferred from WUSTL you can have your app forwarded to QB partner schools.
By the way everyone wants to go to MIT or Yale but many of the QB partners are less competitive. Be sure to take a realistic look at your stats when you forward apps.