Please note that you cannot, under any circumstance, "have" a situation. Always and exclusively, you will find yourself in a situation. Is the difference clear?
Before we get to the punctuation you’re asking about please note that “Please check my website if it looks good” will always be wrong. “Please check whether my website looks good” would work. “Please check my website. Does it look good?” would work. Is the difference clear?
In other circumstances - in ordinary written English - the colons and commas you ask about might be useful or even necessary.
Since the example is "webspeak", either colons or commas might be helpful but neither is needed.