Hola George

Not quite, even if the adjective ends in -o you need to make the adverb (-ly in English, -mente in Spanish) changing that -o into an -a. 

For example:

adjective: rápido (quick)

adverb: rápidamente (quickly)

adjective: lento (slow)

adverb: lentamente (slowly)

You can also think of this differently, as in "take the feminine singular form of the adjective and add -mente": rápida (quick feminine) --> rápidamente,  lenta (slow feminine) --> lentamente

I hope it clarified it.

Saludos

Inma