Worried.

I sent my esa wca form back with quite a bit of medical evidence,(3 weeks ago,) so much so that piffly envelope they provide wasn't sufficient to carry it all.
So I used a large brown envelope and properly addressed it adding what it was in brackets (WCA form) on the front.
And paid for it to be signed for,which it was, I got a screen shot of the signature, and i have the postage certificate. What I want to ask is ,did I make a mistake by not using the envelope they included. Will it make any difference, I remember doing likewise for my Pip form and it seemed alright.But never have before for esa.
TIA.