GiGs is saying that if you want the sheet to be interactive and reactive in Roll20, it needs to be hand written from the ground up.
The HTML export from Excel is really just creating something that will display in a browser. There's no connection to Roll20's backend there, and so no 'character sheet', just a disconnected HTML form.
Imagine buying a letterbox, sticking it on an uninhabited island, and putting a letter in it. That letter isn't going anywhere just because it's in a letterbox - you'll need to find or create a postal service, organise a schedule, make sure the collector understands the destination address, double-check the contents so you don't send the wrong thing etc. etc.
That said - if all the math is ready to go, that's actually very helpful.
Edit - all that said, if you have somewhere you can post the HTML you've ended up with and link it, people can have a look at it and see if there's a quick way of making it usable. It won't be pretty or have repeating sections, roll buttons or anything else that makes a sheet easy to use, but there may be a quick way of turning into a very basic starting point.