After raising his iPad sales estimates to 600,000 to 700,000 over the weekend, Piper Jaffray Senior Research Analyst, Gene Munster, admitted he misgauged the online pre-orders for the device. “We originally estimated online-sales to be about 75% of all iPad sales; however, it appears that online pre-orders made up about 50% of the sales, resulting in a significant unit difference,” said Munster in a note to clients on Monday.

Munster’s original iPad sales estimates were 200-300 thousand for the initial day of sales, which turned out to be more in-line with Apple’s actual sales. Apple announced on Monday it sold more than 300,000 iPads on the first day.

Munster lowered his 2010 sales estimates for the iPad from 5.6 million to 4.3 million. That number is still ahead of his original estimate of 2.7 million units for the year.

It should be noted that the estimate of 5.6 million iPads was based on Munster’s higher, misguided estimates.