Burning your hands could be the least of your problems if you charge to the high side. The can will possibly explode.
I highly recommend that you don't charge based solely on a two bit low side gauge from Wal-Mart. Refrigeration is definitely not a DIY project unless you do a little study and have the right equipment.
There is an excellent book available at ackits.com that is a basic training manual for a/c. They also have equipment and supplies that you might need. Another excellent source is acsource.com. You can access these and a great discussion board where your a/c questions will be answered by pros at; aircondition.com.
Please be careful and don't hurt yourself or destroy your air conditioner.