If you transfer status in US, say F1-H1B, your legal period to stay in US is on the I-94 which is attached to the bottom of I-797, the approval notice. So in the end how long you can stay is determined by the date on I-94, and nothing else. Dig your forms out, and check carefully. If you think the port officer made a mistake, go to local USCIS office ASAP and correct it.
Hope it is not this bad.