"Worthwhile" is an adjective that means that something is worth the time it takes. "Worth" is a noun that means "value". It can also be an adjective in the form "to be worth something" (ex. "This watch is worth $200" or, in my sentence above, "...is worth the time it takes"). So you can only use worthwhile in your sentence.

you could say, The conference I attended yesterday was worthwhile, or, I went to the connference yesterday and it was worth it.

Thank you Candice :D

Worthwhile is correct in this sentence :)