Credit card companies aren't nice. They've an array of tricks to bite your cash.
‘Nearly' paying off in full is impossible.
Repay credit cards in full at the end of the month and (with a few exceptions) no interest is charged. However pay most, but not all, of it off and interest is charged on the whole debt.
Put it like this, spend £1,000 and then repay £980 and you pay a month's interest on the entire £1,000 debt, not just the remaining £20! It's always worth trying to scrape the extra cash to pay off in full.
Interest-free doesn't mean nothing to repay.
Don't confuse a short term interest free offer with nothing to repay, 0% debt is still debt, if you can't afford it to pay it back, don't do it. And remember each card has a set minimum amount (usually 2% or 3% of the balance) you must to repay each month.
Please don't borrow lightly. Plan, budget and prepare you finances to ensure you can make the repayments. If you are trying to borrow more and already in debt, be careful, read ‘Where to Start with Problem Debts' first and ask whether you really need to borrow.
A fine solution
Lenders impose fines for late or missed payments, plus they can cancel special offer interest rates. To beat this, set up a direct debit to pay off the card, even for just for the minimum repayments (or more if you can); you'll never get fined and prevent ruining your credit score.
Yet you should always try and pay more off if you can (see DANGER: Minimum Repayments), and even though you've a direct debit, nothing is stopping you paying by cheque or debit card on top each month.