Does applying in an IPO guarantee me to get certain amount of shares?

No, applying for shares in an IPO or actually bidding for shares in an IPO doesn't give any guarantee to get the shares.

As it's a bidding process, allotment depend on number of bids received in different categories, the price at which investor applied for shares etc.

Once IPO closes, registrar of the issue collect all the bidding information and prepares a ‘Basis of Allotment'. This document provides information about the bids received by verity of investors at different prices and the pattern of allotment.