Extra Safari Browser Window Opens on Startup

Here is probably a dumb question. The script I have below works. It just opens my URL in a new window of Safari instead of loading it into the default window when Safari Opens. How do I resolve this?

set theURL to "http://www.mywebsite.com" tell application "safari" open location theURL end tell

try this syntax

tell application "Safari"
	set URL of document 1 to "http://www.mywebsite.com"
end tell