@Umberto **********
you misunderstand how it works
you are not getting ANY visa when you bounce out/back you you GOT the visa emailed to you once the consulate sent you the email saying the visa was approved.
You're ACTIVATING an entry from it so you get stamped in on it for 90 days
The visa is the PDF file that came in the approval email
You PRINT that out and you show the PDF with your passport when you go to stamp back in and they will stamp you IN to thailand for 90 days FROM that Non-B visa PDF print out you have
Now whether you can bounce out/back to activate that visa entry at the Ranong border by water with Burma would be totally up to the passport control officers at the border when you go to stamp out of thailand. You should be able to